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

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https://hg.mozilla.org/integration/gaia-central/rev/6f8a6769ffd7
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #17130 from etiennesegonzac/bug-981804-will-change-full-screen

Bug 981804 - Don't will-change full screen ancestors app windows. r=vingtetun

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https://hg.mozilla.org/integration/gaia-central/rev/f0f2c0bb9353
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 981804 - Don't will-change full screen ancestors app windows.
Bumping manifests a=b2g-bump