Bumping gaia.json for 2 gaia-1_2 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_2/rev/55a1d00e5e15
Author: John Ford <john@johnford.info>
Desc: bug 930544 - v1.2 uplift
Merge remote-tracking branch 'mcjimenez/v1.2' into v1.2

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https://hg.mozilla.org/integration/gaia-1_2/rev/4a918e37eee7
Author: Gregor Wagner <anygregor@gmail.com>
Desc: Merge pull request #13265 from mcjimenez/bug930544

Bug 930544 - Allow installing applications on several empty screens(cherry picked from commit 82e8266e56b8d7dc94832d2f94c7f4deef658c96)

Conflicts:
	apps/homescreen/js/grid.js