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

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https://hg.mozilla.org/integration/gaia-central/rev/cca21b561090
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #16561 from yurenju/homescreen-975997

Bug 975997 - |APP=homescreen make| doesn't work r=@cctuan

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https://hg.mozilla.org/integration/gaia-central/rev/dd777502b67f
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 975997 - |APP=homescreen make| doesn't work
Bumping manifests a=b2g-bump