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

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https://hg.mozilla.org/integration/gaia-central/rev/fae141e19864
Author: Fernando Jiménez Moreno <ferjmoreno@gmail.com>
Desc: Merge pull request #16753 from 6a68/bug-978275-fxa-test-app-overlay

Bug 978275 - FxA Test App - dismiss overlay after a while. r=ferjm

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https://hg.mozilla.org/integration/gaia-central/rev/b2589e7055ff
Author: Jared Hirsch <ohai@6a68.net>
Desc: Bug 978275 - FxA Test App - dismiss overlay after a while. r=ferjm
Bumping manifests a=b2g-bump