Handle arrays in Grape::Endpoint#expose_params

[fotos]

Since, in ruby-grape/grape#1863, I changed the code that made type a string, the code that generates the appropriate OpenAPI array definitions in grape-swagger broke.

In #expose_params there is a nasty trick (hack?) that removes the brackets from stringified Array classes in order to (recursively) expose the params (introduced here). The change in this PR treats arrays as first class objects.

Unfortunately I can't say I fully understand what's going on, therefore, please guide me and let me know if this is gonna introduce any regressions to existing projects.

This PR works with ruby-grape/grape#1863, thus specs might be broken for HEAD or other versions.

[coveralls]

Coverage decreased (-0.1%) to 99.364% when pulling 917bd8b on fotos:fix-array-handling into e1261f8 on ruby-grape:master.

[LeFnord]

@fotos … please see my comment here #741 (comment)

and many thanks … 👍

[swistaczek]

Hey, is there any chance that this may get merged? cc @LeFnord @fotos