Just thought I would place this here in case anyone else is having permission issues with Ruby bundle installs,
The issue is that ruby bundler is a system install and thus means when running bundle as a user(as you should be doing) you will get permission write errors. The fix is to simply add the below to your bashrc or equivalent
export GEM_HOME="$(ruby -e 'puts Gem.user_dir')"
export PATH="$GEM_HOME/bin:$PATH"