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

========

https://hg.mozilla.org/integration/gaia-central/rev/7b310a78ae68
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Merge pull request #19198 from dominickuo/bug-998911

Bug 998911 - [Settings] Visual update for the volume sliders in sound region, r=crh0716

========

https://hg.mozilla.org/integration/gaia-central/rev/a6fd232929a2
Author: Dominic Kuo <dkuo@mozilla.com>
Desc: Bug 998911 - [Settings] Visual update for the volume sliders in sound region
Bumping manifests a=b2g-bump