Remove the Gemnasium badge

This is a service we no longer use.

README.md

@@ -7,13 +7,11 @@ Delayed::Job
 ============
 [![Gem Version](https://badge.fury.io/rb/delayed_job.png)][gem]
 [![Build Status](https://travis-ci.org/collectiveidea/delayed_job.png?branch=master)][travis]
-[![Dependency Status](https://gemnasium.com/collectiveidea/delayed_job.png?travis)][gemnasium]
 [![Code Climate](https://codeclimate.com/github/collectiveidea/delayed_job.png)][codeclimate]
 [![Coverage Status](https://coveralls.io/repos/collectiveidea/delayed_job/badge.png?branch=master)][coveralls]
 
 [gem]: https://rubygems.org/gems/delayed_job
 [travis]: https://travis-ci.org/collectiveidea/delayed_job
-[gemnasium]: https://gemnasium.com/collectiveidea/delayed_job
 [codeclimate]: https://codeclimate.com/github/collectiveidea/delayed_job
 [coveralls]: https://coveralls.io/r/collectiveidea/delayed_job