Bumping gaia.json for 5 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/12ede7add487
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Merge pull request #15920 from mcav/preview-lock

Bug 966023 - [B2G][Clock][Timer] Sounds previews continue to play from t...

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https://hg.mozilla.org/integration/gaia-central/rev/7f57215527d1
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Use TimerPanel.prototype.onvisibilitychange. r=jugglinmike

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https://hg.mozilla.org/integration/gaia-central/rev/2d16db06d3cd
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Bug 966023 - [B2G][Clock][Timer] Sounds previews continue to play from the timer "Sound list" when locking the device.

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https://hg.mozilla.org/integration/gaia-central/rev/95d29ed3e19f
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #15977 from mikehenrty/bug-966571-retrycount

Bug 966571 - Retry count not shown up in System SIM Dialog, r=arcturus,alive,ferjm

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https://hg.mozilla.org/integration/gaia-central/rev/a0848ecd7a37
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 966571 - Retry count not shown up in System SIM Dialog
Bumping manifests a=b2g-bump