(PDK-1066) Use ruby 2.4.4 with travis

[vinzent]

This aligns with the ruby version provided by the pdk.

[vinzent]

convention: rubocop: lib/puppet/provider/testprovider/testprovider.rb:4:60: Layout/SpaceBeforeFirstArg: Put one space between the method name and the first argument.

is not related to this change.

this class line triggers the warning:

require 'puppet/resource_api/simple_provider'

# Implementation for the testprovider type using the Resource API.
class Puppet::Provider::Testprovider::Testprovider < Puppet::ResourceApi::SimpleProvider
  def get(_context)
    [
...

doesn't make sense to me.

[rodjek]

That rubocop failure was due to a bug in one of rubocop's dependencies.