Add option '--port' to 'rails server' alias.

plugins/rails/rails.plugin.zsh

@@ -42,6 +42,7 @@ alias rp='rails plugin'
 alias ru='rails runner'
 alias rs='rails server'
 alias rsd='rails server --debugger'
+alias rsp='rails server --port'
 
 # Rake aliases
 alias rdm='rake db:migrate'