Fix CI

[dblock]

• On rack.edge nil arguments are now empty String
• rspec 3.10 seems to have a broken expect(subject).to receive(:method).with(hash)

[grape-bot]

	1 Warning
⚠️	Unless you're refactoring existing code or improving documentation, please update CHANGELOG.md.

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

* [#2246](https://github.com/ruby-grape/grape/pull/2246): Fix ci - [@dblock](https://github.com/dblock).

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