Two small improvements

Great project!  I know you haven't updated it recently, but wanted to give this a try anyway.

Two small changes:

* use secure rubygems host in Gemfile (removes a scary warning on bundle install)
* don't use `be` as an alias for `bundle exec` in the README.  I actually have this aliased, but in the interest of being accessible, it probably makes sense to not do it in the README.

Thanks!