Bumping gaia.json for 1 gaia-1_3 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_3/rev/e7991be9540d
Author: Evyatar Amitay <evyatron@gmail.com>
Desc: Merge pull request #15251 from EverythingMe/959134-offline-session-init

[Bug 959134] Fix first-use offline searching [r=ranbena]