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

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https://hg.mozilla.org/integration/gaia-central/rev/1a994a8253ed
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #15250 from crdlc/bug-957971

Bug 957971 - [Download Manager] A notification download failed is displa...

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https://hg.mozilla.org/integration/gaia-central/rev/72573f1b346c
Author: crdlc <crdlc@tid.es>
Desc: Bug 957971 - [Download Manager] A notification download failed is displayed after deleted a stopped or failed download