Update _heroku config arguments (Heroku Client v3)

plugins/heroku/_heroku

@@ -23,8 +23,10 @@ _1st_arguments=(
   "auth\:login":"log in with your heroku credentials"
   "auth\:logout":"clear local authentication credentials"
   "config":"display the config vars for an app"
-  "config\:add":"add one or more config vars"
-  "config\:remove":"remove a config var"
+  "config\:pull":"pull heroku config vars down to the local environment"
+  "config\:push":"push local config vars to heroku"
+  "config\:set":"set one or more config vars"
+  "config\:unset":"unset one or more config vars"
   "db\:push":"push local data up to your app"
   "db\:pull":"pull heroku data down into your local database"
   "domains":"list custom domains for an app"