bundler/setup (LoadError)

On the mac, it is possible that you installed gems to ./vendor/bundle in order to avoid to use SUDO. You can find it if you run gem install bundler and at the end of the output you see the following:

Using turbolinks-source 5.1.0
Using turbolinks 5.1.0
Using uglifier 4.1.4
Bundle complete! 13 Gemfile dependencies, 68 gems now installed.
Bundled gems are installed into `./vendor/bundle`

If this is the case than in your app root directory delete the bundle directory. After this run the following commands:

[sudo] gem install bundler
bundle install

It solved the problem for me

You likely have bundler gem missing.

To get it to work run (first command may need be executed with sudo, depending on your environment):

[sudo] gem install bundler
bundle install