Update Gemfiles
Use `[]=` instead of `merge!` to mutate the current Router scope.

This was broken in Rails 4.2.0+ because the `@scope` object is no longer a Hash
but an internal structure that supports a better override/rollback flow for cases
like this. If we would only support Rails 4.2, this method could be something
like this:

```ruby
def with_devise_exclusive_scope(new_path, new_as, options)
  overrides = { as: new_as, path: new_path, module: nil }
  overrides.merge!(options.slice(:constraints, :defaults, :options))

    @scope = @scope.new(overrides)
  yield
ensure
  @scope = @scope.parent
end
```
Remove missing action warning from the omniauth callbacks route.
Update gemfile with latest Rails changes and Responders 2.