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

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https://hg.mozilla.org/integration/gaia-1_2/rev/66ed88ef78b6
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #14892 from etiennesegonzac/bug-948975-resume-single-conference-group

Bug 948975 - Safeguard to make sure we can always resume a single held conference call. r=rik
(cherry picked from commit 7354e63bc91309895b85ca711baa5caff2991c73)