update rails runner alias to ru

- avoid rr as it is mostly used for restart rails server

plugins/rails3/rails3.plugin.zsh

@@ -14,7 +14,7 @@ alias rdb='_rails_command dbconsole'
 alias rdbm='rake db:migrate db:test:clone'
 alias rg='_rails_command generate'
 alias rp='_rails_command plugin'
-alias rr='_rails_command runner'
+alias ru='_rails_command runner'
 alias rs='_rails_command server'
 alias rsd='_rails_command server --debugger'
 alias devlog='tail -f log/development.log'