Add bundle open alias, which open gem using EDITOR var

plugins/bundler/bundler.plugin.zsh

@@ -3,6 +3,7 @@ alias bi="bundle install"
 alias bl="bundle list"
 alias bu="bundle update"
 alias bp="bundle package"
+alias bo="bundle open"
 
 # The following is based on https://github.com/gma/bundler-exec