Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-2_1/rev/28dabef7d06c
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Merge pull request #27489 from EragonJ/v2.1-bug-1107696

Bug 1107696 - Fix the problem that cannot connect to hidden network, r=crh0716

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https://hg.mozilla.org/integration/gaia-2_1/rev/a9ac3df2e78b
Author: EragonJ <eragonj@eragonj.me>
Desc: Bug 1107696 - Fix the problem that cannot connect to hidden network

Because in wifi_join_hidden panel, we were overriding the wrong
properties and this would make this panel broken after first-time use

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https://hg.mozilla.org/integration/gaia-2_1/rev/a245a14de102
Author: Steve Chung <schung@mozilla.com>
Desc: Bug 1118154 - [FFOS7715 v2.1] [dolphin] FFOS can not receive Cell Broadcast messages on SIM2, r=kgrandon

Conflicts:
	apps/system/js/cell_broadcast_system.js
	apps/system/test/unit/cell_broadcast_system_test.js