Reword upgrade -y comment, improve layout and allow just y.

doc/update/upgrader.md

@@ -19,11 +19,9 @@ __GitLab Upgrader is available only for version 6.4.2 or higher__
 
     cd /home/git/gitlab
     sudo -u git -H ruby script/upgrade.rb
-
-    # it also supports -y option to avouid user input
+    # to perform a non-interactive install (no user input required) you can add -y
     # sudo -u git -H ruby script/upgrade.rb -y
 
-
 ### 3. Start application
 
     sudo service gitlab start

lib/gitlab/upgrader.rb

@@ -17,7 +17,7 @@ module Gitlab
                    prompt("Do you want to upgrade (yes/no)? ", %w{yes no})
                  end
 
-        if answer == "yes"
+        if answer == "yes" || answer == "y"
           upgrade
         else
           exit 0