Disable zsh auto-correct

This is bugging the shit out of me. Especially when it tries to correct
`rspec` (command) to `spec` (directory). I could disable it for some
individual keywords, but actually I haven't found it to be that useful at
all. So turn it all off.
Use shared directory for Bundler

Prevents downloading and installing for every since project, but still
without the need to install them as root or into the default user path.