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

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https://hg.mozilla.org/integration/gaia-central/rev/0a6e7c81947c
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #21809 from yurenju/preferences

Bug 1039219 - Migrate all snippets for preferences in Makefile to preferences.js r=@gduan

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https://hg.mozilla.org/integration/gaia-central/rev/b5984280479f
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 1039219 - Migrate all snippets for preferences in Makefile to preferences.js r=gduan

Conflicts:
	build/preferences.js
Bumping manifests a=b2g-bump