remove binstubs

Using `--binstubs` with `$PATH` is not secure - more details here => http://niczsoft.com/2013/10/please-hack-my-rails/

I have changed the commands for something that will work for everybody and those who use shortcuts will know how to use them.

I also have seen `--binstubs` in other projects, like https://github.com/capistrano/rails ... and few more, but not all (https://github.com/capistrano/bundler) should I open PR for each of them or can someone with commit rights to every of them do the fix?

related capistrano/rvm#17