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

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https://hg.mozilla.org/integration/gaia-central/rev/12b5fea8f2d5
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #13491 from crdlc/bug-935081

[Bug 935081][Download Manager] New shared component DownloadLauncher

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https://hg.mozilla.org/integration/gaia-central/rev/8650c5e32be3
Author: crdlc <crdlc@tid.es>
Desc: [Download Manager] New shared component DownloadLauncher