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

========

https://hg.mozilla.org/integration/gaia-central/rev/cb8a20134671
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #15478 from KevinGrandon/bug_961137_disable_places_test

Bug 961137 - Disable intermittent places test

========

https://hg.mozilla.org/integration/gaia-central/rev/55424079b3b2
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 961137 - Disable intermittent places test
Bumping manifests a=b2g-bump