Add /bin to .gitignore
Add /bin to .gitignore

I'm trying out `bundle install --binstubs` on my local development machine, but don't want to force these binstubs on everyone.

alphagov/whitehall,YOTOV-LIMITED/whitehall,askl56/whitehall,ggoral/whitehall,askl56/whitehall,askl56/whitehall,hotvulcan/whitehall,alphagov/whitehall,hotvulcan/whitehall,robinwhittleton/whitehall,hotvulcan/whitehall,ggoral/whitehall,ggoral/whitehall,YOTOV-LIMITED/whitehall,ggoral/whitehall,robinwhittleton/whitehall,alphagov/whitehall,YOTOV-LIMITED/whitehall,robinwhittleton/whitehall,YOTOV-LIMITED/whitehall,alphagov/whitehall,askl56/whitehall,hotvulcan/whitehall,robinwhittleton/whitehall