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

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https://hg.mozilla.org/integration/gaia-central/rev/4bb50090b876
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #18098 from yurenju/keyboard-makefile

Bug 993835 - Added Makefile for keyboard back r=@cctuan

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https://hg.mozilla.org/integration/gaia-central/rev/77a84375098d
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 993835 - Added Makefile for keyboard back
Bumping manifests a=b2g-bump