Bumping gaia.json for 2 gaia-1_2 revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-1_2/rev/3983cb8cebf5
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #14475 from davidflanagan/bug945376-v1.2

Bug 945376: correctly handle the None alert tone setting

========

https://hg.mozilla.org/integration/gaia-1_2/rev/4cb26c249893
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 945376: correctly handle the None alert tone setting
(cherry picked from commit 19dba5709ee860750765636f298889bf1441d083)