Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-2_0/rev/6c327994ce90
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #21631 from etiennesegonzac/bug-1030433

Bug 1030433 - Always open target=_blank links/window.open outside of the app r=alive

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https://hg.mozilla.org/integration/gaia-2_0/rev/d1d61e81456c
Author: Sam Foster <sfoster@mozilla.com>
Desc: Bug 1019289 - Updated videos including missing 2.25x, via epang. r=me

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https://hg.mozilla.org/integration/gaia-2_0/rev/1591075500c6
Author: Sam Foster <sfoster@mozilla.com>
Desc: Bug 1019289 - Update FTU tutorial videos. r=me
Bumping manifests a=b2g-bump