Bumping gaia.json for 1 gaia-1_2 revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-1_2/rev/2b8f34fb324a
Author: Dave Huseby <dhuseby@mozilla.com>
Desc: Bug 915672 - Modify marionette test driver scripts to add support for gathering power draw data. r=dhunt r=jgriffin