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

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https://hg.mozilla.org/integration/gaia-central/rev/e520ec1919d3
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #13340 from huchengtw-moz/video/Bug_903920_flatfish_ui

Bug 903920 - [Flatfish][Video] support 2 column layout for tablet, r=cctuan

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https://hg.mozilla.org/integration/gaia-central/rev/35e06ab2ebf3
Author: John Hu <johu@mozilla.com>
Desc: Bug 903920 - [Flatfish][Video] support 2 column layout for tablet