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

========

https://hg.mozilla.org/integration/gaia-central/rev/e7c5310e582a
Author: Arthur Chen <crh0716@gmail.com>
Desc: Merge pull request #15459 from cctuan/957100

Bug 957100 - [Settings] add marionette for b2g-improve and feedback page r=crh0716

========

https://hg.mozilla.org/integration/gaia-central/rev/72ab92ec7e3a
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 957100 - [Settings] add marionette for b2g-improve and feedback page
Bumping manifests a=b2g-bump