Update GitHub commit Onebox

This PR updates the GitHub commit onebox to match the GitHub pull request onebox. The existing commit onebox is causing a [bit of confusion](http://meta.discourse.org/t/github-commit-oneboxes-make-me-click-the-wrong-link-everytime/7332/2). The goal is to make it very obvious which link(s) will take you to the commit.

The commit onebox will change from this:

![old-onebox](https://f.cloud.github.com/assets/65323/630038/a1b20d20-d187-11e2-84ed-5b55d7554661.jpg)

To this:

![new-onebox](https://f.cloud.github.com/assets/65323/630037/a1adf4f6-d187-11e2-8630-07bc2857b664.jpg)