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

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https://hg.mozilla.org/integration/gaia-central/rev/ac1a0f1b5429
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #12920 from bebef1987/lock_notif

Bug 927808 - Test notification when the screen is locked

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https://hg.mozilla.org/integration/gaia-central/rev/ed8dcaec64b7
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 927808 - Test notification when the screen is locked