Allow Classes for type declarations inside documentation

[mrmargolis]

Grape requires types to be specified using Classes, not strings. This was problematic when using Entity.documentation to specify params restrictions while also exposing the entity as a Model to grape-swagger.

           module Entities
             class Game < Grape::Entity
                expose :level_name, documentation: { type: String }
             end
           end


          #in a grape endpoint
           params do
             requires :all, using: Entities::Game.documentation
           end

Without this patch the above code causes grape-swagger to consider String distinct from 'string' when type checking for swagger output on Models. This breaks the swagger UI with "this.dataType.toLowerCase is not a function swagger"

[dblock]

This makes sense. Can you please update CHANGELOG and squash these commits? Thanks.

[mrmargolis]

Done. Thanks.