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

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https://hg.mozilla.org/integration/gaia-central/rev/4a67b4e4f948
Author: lissyx <lissyx+github@lissyx.dyndns.org>
Desc: Merge pull request #18709 from lissyx/bug963234

Bug 963234 - Switch to mozNotificationEvent r=mhenretty,alive

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https://hg.mozilla.org/integration/gaia-central/rev/c91eff6ed29f
Author: Alexandre Lissy <lissyx+github@lissyx.dyndns.org>
Desc: Bug 963234 - Switch to mozNotificationEvent r=mhenretty,alive
Bumping manifests a=b2g-bump