Bumping gaia.json for 3 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/6c916d22a128
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 938126 - Python xfail test_gallery_edit_photo failiing gralloc/oom error

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https://hg.mozilla.org/integration/gaia-central/rev/be8740392676
Author: Teodosia Pop <teodosia.pop@gmail.com>
Desc: Merge pull request #13633 from bobsilverberg/emeaddc

Bug 926367 - Add a test to add a new e.me collection

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https://hg.mozilla.org/integration/gaia-central/rev/117dac230c33
Author: Bob Silverberg <bob.silverberg@gmail.com>
Desc: Bug 926367 - Add a test to add a new e.me collection