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

========

https://hg.mozilla.org/integration/gaia-central/rev/8c37833f4969
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #12814 from pivanov/bug-845110

Bug 845110 - Calendar - Create Event Screen Updates r=kgrandon

========

https://hg.mozilla.org/integration/gaia-central/rev/9bb40d427bf3
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 845110 - Calendar - Create Event Screen Updates