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

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https://hg.mozilla.org/integration/gaia-central/rev/db1df4debc98
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #18008 from yurenju/stage5

Bug 897352 - [gaia build system] Transition to a build_stage for assembl...

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https://hg.mozilla.org/integration/gaia-central/rev/ba892a76e1dd
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