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

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https://hg.mozilla.org/integration/gaia-central/rev/d9996c8cd958
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #15903 from crdlc/bug-966463

Bug 966463 - [B2G][Homescreen] Cancelling an app download from Homescree...

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https://hg.mozilla.org/integration/gaia-central/rev/1a4049b50b71
Author: crdlc <crdlc@tid.es>
Desc: Bug 966463 - [B2G][Homescreen] Cancelling an app download from Homescreen will result in a grey icon that has no function after a restart
Bumping manifests a=b2g-bump