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

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https://hg.mozilla.org/integration/gaia-2_0/rev/7539198732ec
Author: lissyx <lissyx+github@lissyx.dyndns.org>
Desc: Merge pull request #20757 from lissyx/bug1017821

Bug 1017821 - Cleanup voicemail notifications on start r=etienne_s

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https://hg.mozilla.org/integration/gaia-2_0/rev/7027fd931171
Author: crdlc <crdlc@tid.es>
Desc: Bug 1029167 - [B2G][2.0][Flame][Smart Collections] Missing Star Button (bookmark) on Smart Collection App

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https://hg.mozilla.org/integration/gaia-2_0/rev/5ca83062873c
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #20917 from lightsofapollo/bug-1029329

Bug 1029329 - After downloading an app with a role we consider hidden re...
Bumping manifests a=b2g-bump