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

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https://hg.mozilla.org/integration/gaia-central/rev/560f88488bd3
Author: punamdahiya <punamdahiya@yahoo.com>
Desc: Merge pull request #23870 from punamdahiya/Bug1063291

Bug1063291-[Video]-Fix back button in video pick activity r=wilsonpage

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https://hg.mozilla.org/integration/gaia-central/rev/15dbde58c87c
Author: Punam Dahiya <punamdahiya@yahoo.com>
Desc: Bug1063291-[Video]-Fix back button in video pick activity r=wilsonpage
Bumping manifests a=b2g-bump