Switch to 2013 now that it's what's on the bots

Chromium only supports 2013 now, and the bots no longer have older versions.

Support for other versions still maintained, just not on buildbot.

R=sbaig1@bloomberg.net

Review URL: https://codereview.chromium.org/647043003

git-svn-id: http://gyp.googlecode.com/svn/trunk@1996 78cadc50-ecff-11dd-a971-7dbc132099af