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

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https://hg.mozilla.org/integration/gaia-central/rev/20661b944c2e
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #17514 from alivedise/bugzilla/961800_master_merging/child-window-factory

Bug 961800 - Implement Child Window Factory. r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/be865a491ba3
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 961800 - Implement Child Window Factory.

Conflicts:
	apps/system/js/app_transition_controller.js
	apps/system/js/app_window.js
	apps/system/js/app_window_manager.js
	apps/system/js/cards_view.js
	apps/system/style/window.css
Bumping manifests a=b2g-bump