Update .gitignore and .keep files

https://github.com/thoughtbot/suspenders/commit/937459a9f9463d97edfbc34b
ae8a7d28ba1873eb
Remove dependency on `hub` gem

https://github.com/thoughtbot/suspenders/commit/4bfcc1304dfdb5d8ff5e3751
9751db632c103b4f
Update capybara-webkit gem version