Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/e28e9e49c064
Author: Zac <zac@zac-ThinkPad-X1.(none)>
Desc: Bug 938612 - Disable intermittent clock tests on Travis
Bumping manifests a=b2g-bump