Fix request params key duplicates.

The problem is that `env['action_dispatch.request.parameters']` has strings as its keys. That leads to having params like `{:controller => nil, :action => nil, :format =>nil, "controller"=>"flights", "action"=>"index"}`. Then it's converted into json by multi_json, and the behavior of json adapters differ in this case. That how Oj behaves:

    >> puts Oj.dump(:controller => nil, :action => nil, :format =>nil, "controller"=>"flights", "action"=>"index")
    {"controller":null,"action":null,"format":null,"controller":"flights","action":"index"}

And that's valid json. Such json used to be parsed successfully by the Rollbar server, but three days ago it started to throw this:

    [Rollbar] Sending payload
    [Rollbar] Got unexpected status code from Rollbar api: 403
    [Rollbar] Response: {
      "err": 1,
      "message": "access token not found: undefined"
    }

Whilst having no duplicates leads to a successful payload sending. So I guess that JSON parser was changed on the Rollbar server three days ago.