Bumping gaia.json for 6 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/7c7d1648ba4e
Author: Luke Chang <lchang@mozilla.com>
Desc: Merge pull request #17638 from luke-chang/971458_instantiable_app_window_factory_v2

Bug 971458 - [System2] Instantiable AppWindowFactory, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/ed773fec11b6
Author: Luke Chang <lchang@mozilla.com>
Desc: Bug 971458 - [System2] Instantiable AppWindowFactory

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https://hg.mozilla.org/integration/gaia-central/rev/b068c13545a6
Author: EragonJ <eragonj@eragonj.me>
Desc: Merge pull request #17573 from EragonJ/bug-960861-fix

Bug 960861 - mozMobileConnections should not be requisites for airplane ...

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https://hg.mozilla.org/integration/gaia-central/rev/8bdf0d4988be
Author: EragonJ <eragonj@eragonj.me>
Desc: Bug 960861 - mozMobileConnections should not be requisites for airplane ...

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https://hg.mozilla.org/integration/gaia-central/rev/63dff6cccf50
Author: Luke Chang <lchang@mozilla.com>
Desc: Merge pull request #17680 from luke-chang/988270_appwindowmanager_cause_unit_test_failed

Bug 988270 - The unit test of AppWindowManager will break other tests in system app, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/15d0692ac4f3
Author: Luke Chang <lchang@mozilla.com>
Desc: Bug 988270 - The unit test of AppWindowManager will break other tests in system app
Bumping manifests a=b2g-bump