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

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https://hg.mozilla.org/integration/gaia-central/rev/da5e6f9984ac
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #16069 from cctuan/968667

Bug 968668 - Add Makefile for browser

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https://hg.mozilla.org/integration/gaia-central/rev/cf5920a2dfa0
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 968668 - Add Makefile for browser
Bumping manifests a=b2g-bump