Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/3b7db4e019c8
Author: Florin Strugariu <bebef_1987@yahoo.com>
Desc: Merge pull request #20669 from zacc/bug_1026424_gallery

Bug 1026424 - Remove frame switching in gallery app tests where possible

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https://hg.mozilla.org/integration/gaia-central/rev/cdef5f3c62c3
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1026424 - Remove frame switching in gallery app tests where possible

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https://hg.mozilla.org/integration/gaia-central/rev/2e2c2138fb3a
Author: AndreiH <andrei.hutusoru@softvision.ro>
Desc: Merge pull request #20683 from zacc/bug_1025996

Bug 1025996 -  Intermittent test_export_contacts_to_sdcard.py

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https://hg.mozilla.org/integration/gaia-central/rev/3b1fedb060be
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1025996 -  Intermittent test_export_contacts_to_sdcard.py
Bumping manifests a=b2g-bump