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

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https://hg.mozilla.org/integration/gaia-central/rev/3ff89cdffb83
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #13014 from jrburke/bug802643-email-activity-return

Bug 802643 - [email] Compose/share activities are unable to return to calling app once message is sent r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/5c25e7eab3a7
Author: jrburke <jrburke@gmail.com>
Desc: Bug 802643 - [email] Compose/share activities are unable to return to calling app once message is sent