Fix stub authentications#create method

As per comment at
http://railscasts.com/episodes/235-omniauth-part-1?view=comments#comment_153390

app/controllers/authentications_controller.rb

@@ -40,7 +40,8 @@ class AuthenticationsController < ApplicationController
   # POST /authentications
   # POST /authentications.json
   def create
-    render :text => request.env["omniauth.auth."].to_yaml
+    auth = request.env['omniauth.auth']
+    render :text => auth.to_yaml
   end
 
   # PUT /authentications/1