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

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https://hg.mozilla.org/integration/gaia-central/rev/308e4c386829
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #15096 from gnaneswar/Defect_953402

Bug 953402 - [hamachi] Video file is incorrectly shown as .jpg in Galler..., r=johnhu

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https://hg.mozilla.org/integration/gaia-central/rev/d67e297adf30
Author: Gnaneswar Devuni <gnaneswar.devuni@accenture.com>
Desc: Bug 953402 - [hamachi] Video file is incorrectly shown as .jpg in Gallery app; r=reviews