Imagine a typical use case for grb:
* User moves to a project dir (~/myproj)
* User uses grb (grb create funtimes)
* grb executes Bundler.setup, which munges Ruby's load path to match myproj's Gemfile.lock
* grb tries to require "rainbow," which isn't in myproj's Gemfile.lock
* grb dies
Gem dependencies are better handled by Rubygems during install, and later by Bundler when running against an
actual app's Gemfile.