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

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https://hg.mozilla.org/integration/gaia-2_1/rev/476dd0a159a7
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #25357 from cctuan/1082864

Bug 1082864 - TypeError: evt is null at: app://system.gaiamobile.org/js/modal_dialog.js line: 250

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https://hg.mozilla.org/integration/gaia-2_1/rev/3072c2a8c720
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 1082864 - TypeError: evt is null at: app://system.gaiamobile.org/js/modal_dialog.js line: 250
Bumping manifests a=b2g-bump