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

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https://hg.mozilla.org/integration/gaia-central/rev/7412c36923b5
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #14742 from alivedise/bugzilla/948596_master_v3/activity-window-size

Bug 948596 - fullscreen state of activity window

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https://hg.mozilla.org/integration/gaia-central/rev/b65f999adbe2
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 948596 - fullscreen state of activity window