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

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https://hg.mozilla.org/integration/gaia-central/rev/f96fce93bc62
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #15512 from huchengtw-moz/gallery/Bug_960215-gallery-open-activity-rotation

Bug 960215 - [B2G][Messages] Image-attachment does not fill the screen i..., r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/4e53e832be20
Author: John Hu <johu@mozilla.com>
Desc: Bug 960215 - [B2G][Messages] Image-attachment does not fill the screen in landscape orientation
Bumping manifests a=b2g-bump