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

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https://hg.mozilla.org/integration/gaia-central/rev/6b946f821121
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #21471 from robertbindar/master

Bug 1030310 - [B2G][Email] Device does not vibrate upon receiving an email notification while in sleep mode

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https://hg.mozilla.org/integration/gaia-central/rev/db96c670a02e
Author: robertbindar <robertbindar@gmail.com>
Desc: Bug - 1030310 disable vibration for email notification when the phone is asleep r=mhenretty
Bumping manifests a=b2g-bump