Add a fail spec for #705

[darren987469]

Add a fail spec for #705

Failures:

  1) desc is_array option in hash style
     Failure/Error: is_array true

     NoMethodError:
       undefined method `is_array' for #<#<Class:0x00007fc42dd0c660>:0x00007fc42dd07980>
       Did you mean?  is_a?
     # ./spec/issues/705_is_array_not_supported_in_desc_block_spec.rb:20:in `block (5 levels) in <top (required)>'
    ...

[coveralls]

Coverage remained the same at 99.204% when pulling 506079e on darren987469:fix_is_array_option_in_desc_block into cdc2087 on ruby-grape:master.

[ysv]

@darren987469 notice that also it overrides hash options in block which looks strange for me too
https://github.com/ruby-grape/grape-swagger/pull/706/files#diff-e2856c84b5197a90f6d3298a589c09d8R14

[grape-bot]

	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:

* [#707](https://github.com/ruby-grape/grape-swagger/pull/707): Add a fail spec for #705 - [@darren987469](https://github.com/darren987469).

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[darren987469]

@LeFnord is_array is supported in the latest grape. Test failed in the older version of grape.