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

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https://hg.mozilla.org/integration/gaia-2_0/rev/4fc40ab9857d
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #16919 from gittup/bug-917630

Bug 917630 - Allow unlimited keypresses when on a call r=etienne
Bumping manifests a=b2g-bump
Bug 1003893 - Ensure that the delete of RasterImage occurs on the main thread. r=seth, a=1.4+

Dispatch nsRefPtr<RasterImage> to the main thread by NS_ProxyRelease
to avoid RasterImage from being destructed by the DecodeJob thread.
(If gMultithreadedDecoding is true.)
Therefore, DiscardTracker can safely access RasterImage::Discard()
by the raw pointer in DiscardTracker::Node.