Update rubocop to version 0.22.0

Gemfile.lock

@@ -145,7 +145,7 @@ GEM
     remotipart (1.2.1)
     rest-client (1.6.7)
       mime-types (>= 1.16)
-    rubocop (0.21.0)
+    rubocop (0.22.0)
       json (>= 1.7.7, < 2)
       parser (~> 2.1.9)
       powerpack (~> 0.0.6)

app/controllers/application_controller.rb

@@ -8,10 +8,8 @@ class ApplicationController < ActionController::Base
 protected
 
   def set_flash_from_params
-    if params[:flash]
-      params[:flash].each do |key, message|
-        flash.now[key.to_sym] = message
-      end
+    params.fetch(:flash, []).each do |key, message|
+      flash.now[key.to_sym] = message
     end
   end