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

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https://hg.mozilla.org/integration/gaia-central/rev/28d7e6d4420e
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #14682 from huchengtw-moz/gallery/Bug_949857_make_delete_consistent

Bug 949857 - [Gallery]Red 'Delete' shown when deleting in multiple selec..., r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/9469b905f084
Author: John Hu <johu@mozilla.com>
Desc: Bug 949857 - [Gallery]Red 'Delete' shown when deleting in multiple selection mode, blue "Ok" shown when deleting in fullscreen mode