Add Drone to CI Service Data.

This adds support for [Drone](https://github.com/drone/drone).  The Drone test coverage env vars are not documented, but [exist here](https://github.com/drone/drone/blob/master/pkg/build/build.go#L496-L502).

![screen shot 2014-08-14 at 7 59 04 pm](https://cloud.githubusercontent.com/assets/90807/3928706/04bb51da-240f-11e4-8366-9de8e2e00e01.png)