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

========

https://hg.mozilla.org/integration/gaia-central/rev/8c153b0618e4
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #15619 from pivanov/bug-935095

Bug 935095 - [Gallery] 1.3 Back button position not to spec

========

https://hg.mozilla.org/integration/gaia-central/rev/746bc70f1a51
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 935095 - [Gallery] 1.3 Back button position not to spec
Bumping manifests a=b2g-bump