Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/c9674d674172
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #17369 from yurenju/nfc

Bug 963556: Update NFC Manager, Handover to use new shared nfc_utils.js. r=@alivedise

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https://hg.mozilla.org/integration/gaia-central/rev/215146db2ced
Author: Garner Lee <garner.lee@telekom.com>
Desc: Bug 963556: Update NFC Manager, Handover to use new shared nfc_utils.js.

Conflicts:
	apps/system/js/nfc_handover_manager.js
	apps/system/js/nfc_manager_utils.js

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https://hg.mozilla.org/integration/gaia-central/rev/6ece05f395b5
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #17363 from yurenju/stage2

Bug 897352 - [gaia build system] Transition to a build_stage for assembl... r=@ochameau

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https://hg.mozilla.org/integration/gaia-central/rev/42026d903e61
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 897352 - [gaia build system] Transition to a build_stage for assembling apps

Conflicts:
	Makefile
	apps/communications/build/build.js
	build/copy-build-stage-manifest.js
	build/test/integration/distribution.test.js
	build/utils-xpc.js
	build/utils.js
	build/webapp-manifests.js
Bumping manifests a=b2g-bump