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

========

https://hg.mozilla.org/integration/gaia-2_0/rev/e502c983c4e5
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Merge pull request #23926 from jrburke/bug915643-email-clear-notifications-v2.0

Bug 915643 - v2.0 [Email] Clear old notifications once Notification.get is available r=asuth a=bajaj

========

https://hg.mozilla.org/integration/gaia-2_0/rev/215b9167cded
Author: jrburke <jrburke@gmail.com>
Desc: Bug 915643 - v2.0 [Email] Clear old notifications once Notification.get is available r=asuth a=bajaj
Bumping manifests a=b2g-bump