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

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https://hg.mozilla.org/integration/gaia-central/rev/537a1ebbcaa7
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #12559 from qdot/922394-notification-integration

Bug 922394 - Add skipped test for notification app integration test

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https://hg.mozilla.org/integration/gaia-central/rev/5908df26c6e1
Author: Kyle Machulis <kyle@nonpolynomial.com>
Desc: Bug 922394 - Add skipped test for notification app integration test