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

========

https://hg.mozilla.org/integration/gaia-central/rev/d8a42299ad49
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #20842 from vingtetun/homescreen-on-nightly-race

Bug 1027555 - [Vertical Homescreen] No icons on homescreen with DEBUG=1 ...

========

https://hg.mozilla.org/integration/gaia-central/rev/f5ff909b584b
Author: Vivien Nicolas <vnicolas@mozilla.com>
Desc: Bug 1027555 - [Vertical Homescreen] No icons on homescreen with DEBUG=1 mode on nightly. r=me
Bumping manifests a=b2g-bump