Correct README to remove postgres vendor in example
Correct README to remove postgres vendor in example

heroku/heroku-buildpack-pgbouncer,musicglue/heroku-buildpack-postgresql,BetterWorks/heroku-buildpack-pgbouncer,Shyp/heroku-buildpack-pgbouncer,rmoorman/heroku-buildpack-pgbouncer,agriffis/heroku-buildpack-pgbouncer,gregburek/heroku-buildpack-postgresql,realtymaps/heroku-buildpack-pgbouncer,Yobota/heroku-buildpack-pgbouncer