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

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https://hg.mozilla.org/integration/gaia-central/rev/479cc788f720
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #17942 from snowmantw/issue937442-lockscreen-window

Bug 937442 - (lockscreen-window) [Window Management] Implement LockscreenWindow to manage LockScreen.

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https://hg.mozilla.org/integration/gaia-central/rev/f383508dafdb
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 937442 - (lockscreen-window) [Window Management] Implement LockscreenWindow to manage LockScreen.
Bumping manifests a=b2g-bump