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

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https://hg.mozilla.org/integration/gaia-central/rev/9cb7174fcd56
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #15983 from crdlc/bug-962474

Bug 962474 - [Download Manager] Confirmation screen is not displayed aft...

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https://hg.mozilla.org/integration/gaia-central/rev/72511316d309
Author: crdlc <crdlc@tid.es>
Desc: Bug 962474 - [Download Manager] Confirmation screen is not displayed after trying delete a file
Bumping manifests a=b2g-bump