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

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https://hg.mozilla.org/integration/gaia-central/rev/170eb4111b2e
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Merge pull request #18591 from mcav/css

Bug 991453 - [Sora][Clock]MS flashed a white screen when press power key... r=gaye

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https://hg.mozilla.org/integration/gaia-central/rev/4e3c55b8a989
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Bug 991453 - [Sora][Clock]MS flashed a white screen when press power key to light screen.

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https://hg.mozilla.org/integration/gaia-central/rev/a00f88fd4297
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Merge pull request #18301 from mcav/intermittent-failing

Bug 990798 - [Clock] Disable intermittent failing test, Alarm Update Nam... r=gaye

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https://hg.mozilla.org/integration/gaia-central/rev/98d78f5bfb4a
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Bug 990798 - [Clock] Disable intermittent failing test, Alarm Update Name and Time.
Bumping manifests a=b2g-bump