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

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https://hg.mozilla.org/integration/gaia-1_4/rev/db8fbf27475a
Author: Diego Marcos <diego.marcos@gmail.com>
Desc: Merge pull request #20643 from dmarcos/bug1024692

Bug1024692

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https://hg.mozilla.org/integration/gaia-1_4/rev/e38e90540048
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 1024692: limit image decode size to 3mp on 256mb devices
Bumping manifests a=b2g-bump