Added spec to demonstrate bug with nested requirements.

[darrellnash]

I believe there's a bug that was introduced sometime after Grape 0.13 (we were running a very old version). We have several nested namespaces that have requirements to allow for dots in the path parameters.

e.g. /:user_id/:attr_id, where both :user_id and :attr_id can have dots in them.

When I upgraded to the latest Grape, these stopped working for the first namespace (:user_id) - it appears it's because when you pass in a requirements hash on a route, it replaces any existing requirements on the wrapping namespace.

This spec demonstrates the expected (and previous) behavior, especially the last test case which is failing against master.

A simplified example:

With:

namespace ':user_id', requirements: { user_id: %r{[^\/]+} } do
  get ':attr_id',    requirements: { attr_id: %r{[^\/]+} } do
    "#{params[:user_id]}/#{params[:attr_id]}"
  end
end

Expected:

GET /user.with.dots/attribute.with.dots should work.

Current behavior:

GET /user.with.dots/attribute.with.dots returns a 404 error.

[grape-bot]

	1 Error
🚫	The TOC found in README.md doesn’t match the sections of the file.

	1 Warning
⚠️	Unless you’re refactoring existing code, please update CHANGELOG.md.

	1 Message
📖	We really appreciate pull requests that demonstrate issues, even without a fix. That said, the next step is to try and fix the failing tests!

Here's an example of a CHANGELOG.md entry:

* [#1783](https://github.com/ruby-grape/grape/pull/1783): Added spec to demonstrate bug with nested requirements - [@darrellnash](https://github.com/darrellnash).

Here's the expected TOC for README.md:

# Table of Contents

- [What is Grape?](#what-is-grape)
- [Stable Release](#stable-release)
- [Project Resources](#project-resources)
- [Installation](#installation)
- [Basic Usage](#basic-usage)
- [Mounting](#mounting)
  - [Rack](#rack)
  - [ActiveRecord without Rails](#activerecord-without-rails)
  - [Alongside Sinatra (or other frameworks)](#alongside-sinatra-or-other-frameworks)
  - [Rails](#rails)
  - [Modules](#modules)
- [Versioning](#versioning)
  - [Path](#path)
  - [Header](#header)
  - [Accept-Version Header](#accept-version-header)
  - [Param](#param)
- [Describing Methods](#describing-methods)
- [Parameters](#parameters)
  - [Params Class](#params-class)
  - [Declared](#declared)
  - [Include Parent Namespaces](#include-parent-namespaces)
  - [Include Missing](#include-missing)
- [Parameter Validation and Coercion](#parameter-validation-and-coercion)
  - [Supported Parameter Types](#supported-parameter-types)
  - [Integer/Fixnum and Coercions](#integerfixnum-and-coercions)
  - [Custom Types and Coercions](#custom-types-and-coercions)
  - [Multipart File Parameters](#multipart-file-parameters)
  - [First-Class JSON Types](#first-class-json-types)
  - [Multiple Allowed Types](#multiple-allowed-types)
  - [Validation of Nested Parameters](#validation-of-nested-parameters)
  - [Dependent Parameters](#dependent-parameters)
  - [Group Options](#group-options)
  - [Alias](#alias)
  - [Built-in Validators](#built-in-validators)
    - [allow_blank](#allow_blank)
    - [values](#values)
    - [except_values](#except_values)
    - [regexp](#regexp)
    - [mutually_exclusive](#mutually_exclusive)
    - [exactly_one_of](#exactly_one_of)
    - [at_least_one_of](#at_least_one_of)
    - [all_or_none_of](#all_or_none_of)
    - [Nested mutually_exclusive, exactly_one_of, at_least_one_of, all_or_none_of](#nested-mutually_exclusive-exactly_one_of-at_least_one_of-all_or_none_of)
  - [Namespace Validation and Coercion](#namespace-validation-and-coercion)
  - [Custom Validators](#custom-validators)
  - [Validation Errors](#validation-errors)
  - [I18n](#i18n)
  - [Custom Validation messages](#custom-validation-messages)
    - [presence, allow_blank, values, regexp](#presence-allow_blank-values-regexp)
    - [all_or_none_of](#all_or_none_of-1)
    - [mutually_exclusive](#mutually_exclusive-1)
    - [exactly_one_of](#exactly_one_of-1)
    - [at_least_one_of](#at_least_one_of-1)
    - [Coerce](#coerce)
    - [With Lambdas](#with-lambdas)
    - [Pass symbols for i18n translations](#pass-symbols-for-i18n-translations)
    - [Overriding Attribute Names](#overriding-attribute-names)
    - [With Default](#with-default)
- [Headers](#headers)
- [Routes](#routes)
- [Helpers](#helpers)
- [Path Helpers](#path-helpers)
- [Parameter Documentation](#parameter-documentation)
- [Cookies](#cookies)
- [HTTP Status Code](#http-status-code)
- [Redirecting](#redirecting)
- [Recognizing Path](#recognizing-path)
- [Allowed Methods](#allowed-methods)
- [Raising Exceptions](#raising-exceptions)
  - [Default Error HTTP Status Code](#default-error-http-status-code)
  - [Handling 404](#handling-404)
- [Exception Handling](#exception-handling)
    - [Rescuing exceptions inside namespaces](#rescuing-exceptions-inside-namespaces)
    - [Unrescuable Exceptions](#unrescuable-exceptions)
    - [Exceptions that should be rescued explicitly](#exceptions-that-should-be-rescued-explicitly)
  - [Rails 3.x](#rails-3x)
- [Logging](#logging)
- [API Formats](#api-formats)
  - [JSONP](#jsonp)
  - [CORS](#cors)
- [Content-type](#content-type)
- [API Data Formats](#api-data-formats)
- [JSON and XML Processors](#json-and-xml-processors)
- [RESTful Model Representations](#restful-model-representations)
  - [Grape Entities](#grape-entities)
  - [Hypermedia and Roar](#hypermedia-and-roar)
  - [Rabl](#rabl)
  - [Active Model Serializers](#active-model-serializers)
- [Sending Raw or No Data](#sending-raw-or-no-data)
- [Authentication](#authentication)
  - [Basic and Digest Auth](#basic-and-digest-auth)
  - [Register custom middleware for authentication](#register-custom-middleware-for-authentication)
- [Describing and Inspecting an API](#describing-and-inspecting-an-api)
- [Current Route and Endpoint](#current-route-and-endpoint)
- [Before and After](#before-and-after)
- [Anchoring](#anchoring)
- [Using Custom Middleware](#using-custom-middleware)
  - [Grape Middleware](#grape-middleware)
  - [Rails Middleware](#rails-middleware)
  - [Remote IP](#remote-ip)
- [Writing Tests](#writing-tests)
  - [Writing Tests with Rack](#writing-tests-with-rack)
    - [RSpec](#rspec)
    - [Airborne](#airborne)
    - [MiniTest](#minitest)
  - [Writing Tests with Rails](#writing-tests-with-rails)
    - [RSpec](#rspec-1)
    - [MiniTest](#minitest-1)
  - [Stubbing Helpers](#stubbing-helpers)
- [Reloading API Changes in Development](#reloading-api-changes-in-development)
  - [Reloading in Rack Applications](#reloading-in-rack-applications)
  - [Reloading in Rails Applications](#reloading-in-rails-applications)
- [Performance Monitoring](#performance-monitoring)
  - [Active Support Instrumentation](#active-support-instrumentation)
    - [endpoint_run.grape](#endpoint_rungrape)
    - [endpoint_render.grape](#endpoint_rendergrape)
    - [endpoint_run_filters.grape](#endpoint_run_filtersgrape)
    - [endpoint_run_validators.grape](#endpoint_run_validatorsgrape)
    - [format_response.grape](#format_responsegrape)
  - [Monitoring Products](#monitoring-products)
- [Contributing to Grape](#contributing-to-grape)
- [License](#license)
- [Copyright](#copyright)

Generated by 🚫 danger

[dblock]

Looks like a totally legit bug. Now that there's a spec, try a fix @darrellnash ! :)

The TOC thing is probably unrelated because danger-toc got automatically upgraded and we should take care of it soon (anyone feel free to contribute).

[darrellnash]

Fixed by @darren987469 in #1788. Closing this PR.