Specified :require => 'drip' for Gemfile inclusion

The previous way of including the gem into `Gemfile` didn't work, because the correct file to `require` is `lib/drip.rb` (and not `lib/drip-ruby.rb`)
Merge pull request #11 from yas4891/patch-1

Specified :require => 'drip' for Gemfile inclusion
Add auth via OAuth access tokens (fixes #12)