Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/b2a0e18f6040
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #15648 from etiennesegonzac/bug-907112-lockscreen-too-easy-unlock

Bug 907112 - Prevent the phone from unlocking in my pants r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/ac0d41d60fcb
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 907112 - Prevent the phone from unlocking in my pants
* Reset the slide detection if a new touch point appears
* Better state cleanup

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https://hg.mozilla.org/integration/gaia-central/rev/84a54b465e0e
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 956780 - In gaia_apps atoms, wait for appopen event instead of apploadtime/appopened. r=dhunt
Bumping manifests a=b2g-bump