Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/a7c17d6cce9c
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #17171 from gaye/bug-857284

Bug 857284 - When multiple alarms are available to fire for a calendar event, fire only one notification r=millermedeiros

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https://hg.mozilla.org/integration/gaia-central/rev/b3d62526d892
Author: Gareth Aye <gaye@mozilla.com>
Desc: Bug 857284 - When multiple alarms are available to fire for a calendar event, fire only one notification

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https://hg.mozilla.org/integration/gaia-central/rev/5abdb17d86d1
Author: Gregor Wagner <anygregor@gmail.com>
Desc: Merge pull request #17208 from gregorwagner/tiling

Bug 972779 - [Tarako] Saving picture after editing cause Gallery stop. C...

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https://hg.mozilla.org/integration/gaia-central/rev/0a13503fde1e
Author: Gregor Wagner <anygregor@gmail.com>
Desc: Bug 972779 - [Tarako] Saving picture after editing cause Gallery stop. Change tiling size to 512. r=dflanagen
Bumping manifests a=b2g-bump