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

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https://hg.mozilla.org/integration/gaia-central/rev/53c6a2b0bf4c
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #13385 from zacc/bug_935052_1

Bug 930532 - Python use self.apps.displayed_app in Gallery app object

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https://hg.mozilla.org/integration/gaia-central/rev/08def37fa403
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 930532 - Python use self.apps.displayed_app in Gallery app object