Features/create response

1. Gemfile: Had to remove ruby '2.0.0' in order to run "rails s" on local host
2. Added response partial form and updated controller
3. In order for partial (_form.html.erb) to work. Please update the following in "rants":

I. views/rants/show.html.erb
```
<div class="response-form">
  <div class="errors"></div>
  <%= render 'responses/form', rant: @rant, response: @response %>
</div>
```

II. controllers/rants_controller.rb
```
def show #get particular rant
  @rant = Rant.find(params[:id])
  @responses = @rant.responses
  @response = @rant.responses.build
end
```