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

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https://hg.mozilla.org/integration/gaia-2_0/rev/6db7de95e43d
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1023426 - [Vertical] Remove zoom feature r=me

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https://hg.mozilla.org/integration/gaia-2_0/rev/d53234906be7
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #20374 from davidflanagan/bug996398-v2.0

Bug996398 v2.0

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https://hg.mozilla.org/integration/gaia-2_0/rev/f177a8b8df0b
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #20321 from davidflanagan/bug996398

Bug 996398: use fastSeek() in the Video app(cherry picked from commit bfc48b690164b89dededb8ccf74f4a4f3ae02977)
Bumping manifests a=b2g-bump