Fix new rubocop warnings

.rubocop.yml

@@ -96,12 +96,6 @@ Style/MixinUsage:
     - 'bin/setup'
     - 'bin/update'
 
-Style/RedundantCondition:
-  Exclude:
-    - 'app/controllers/messages_controller.rb'
-    - 'app/controllers/sessions_controller.rb'
-    - 'app/controllers/users_controller.rb'
-
 Style/StringLiterals:
   EnforcedStyle: double_quotes
 

app/controllers/messages_controller.rb

@@ -121,11 +121,7 @@ class MessagesController < ApplicationController
 
       referer = safe_referer(params[:referer]) if params[:referer]
 
-      if referer
-        redirect_to referer
-      else
-        redirect_to :action => :inbox
-      end
+      redirect_to referer || { :action => :inbox }
     end
   rescue ActiveRecord::RecordNotFound
     @title = t "messages.no_such_message.title"

app/controllers/sessions_controller.rb

@@ -38,11 +38,7 @@ class SessionsController < ApplicationController
 
       referer = safe_referer(params[:referer]) if params[:referer]
 
-      if referer
-        redirect_to referer
-      else
-        redirect_to :controller => "site", :action => "index"
-      end
+      redirect_to referer || { :controller => "site", :action => "index" }
     end
   end
 

app/controllers/users_controller.rb

@@ -136,11 +136,7 @@ class UsersController < ApplicationController
     if current_user
       # The user is logged in already, so don't show them the signup
       # page, instead send them to the home page
-      if @referer
-        redirect_to @referer
-      else
-        redirect_to :controller => "site", :action => "index"
-      end
+      redirect_to @referer || { :controller => "site", :action => "index" }
     elsif params.key?(:auth_provider) && params.key?(:auth_uid)
       self.current_user = User.new(:email => params[:email],
                                    :email_confirmation => params[:email],