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

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https://hg.mozilla.org/integration/gaia-1_3/rev/77aa5f6ed261
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #19994 from JerryShih/bug-1008026-wallpaper-flickering-1.3

Bug 1008026 - show thumbnail instead of full size image, r=djf

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https://hg.mozilla.org/integration/gaia-1_3/rev/051b41c14caa
Author: Jerry Shih <hshih@mozilla.com>
Desc: Bug 1008026 - show thumbnail instead of full size image for v1.3
Bumping manifests a=b2g-bump