Bumping gaia.json for 2 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/4ec153439e43
Author: Bob Silverberg <bob.silverberg@gmail.com>
Desc: Merge pull request #14126 from viorelaioia/bug_943579_v1.2

Bug 943579 - override timeout in wait_for_notification_toaster_not_displ...

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https://hg.mozilla.org/integration/gaia-1_2/rev/874b5b2a4b83
Author: Viorela Ioia <viorelaioia@gmail.com>
Desc: Bug 943579 - override timeout in wait_for_notification_toaster_not_displayed()