remove bundler version from CI setup
remove bundler version from CI setup

Scalingo/nodejs-buildpack,heroku/heroku-buildpack-nodejs,Scalingo/nodejs-buildpack,Scalingo/nodejs-buildpack,heroku/heroku-buildpack-nodejs,heroku/heroku-buildpack-nodejs,Scalingo/nodejs-buildpack,heroku/heroku-buildpack-nodejs,Scalingo/nodejs-buildpack,heroku/heroku-buildpack-nodejs