Update GitHub and Travis references in README.md

Hello @dpup, 

Please review the following commits I made in branch 'jcrosby-update-readme'.

e5b332b2a60ed899046ca989564f3b572c83fdb7 (2014-12-02 19:59:42 -0800)
Update GitHub and Travis references in README.md
* Obvious -> Medium

R=@dpup