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

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https://hg.mozilla.org/integration/gaia-central/rev/a109df6bf6ec
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #15046 from viorelaioia/bug_956737

Bug 956737 - Investigate and fix test_gallery_delete_image failure

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https://hg.mozilla.org/integration/gaia-central/rev/fdf9998c44ce
Author: Viorela Ioia <viorelaioia@gmail.com>
Desc: Bug 956737 - Investigate and fix test_gallery_delete_image failure