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

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https://hg.mozilla.org/integration/gaia-central/rev/8d90913d9205
Author: Gregor Wagner <anygregor@gmail.com>
Desc: Merge pull request #14799 from bebef1987/disable_persona

Bug 951570 - Disable persona tests they failing because of http://personatestuser.org/

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https://hg.mozilla.org/integration/gaia-central/rev/3e9a9460838f
Author: Bebe <bebe@mozilla.ro>
Desc: Bug 951570 - Disable persona tests they failing because of http://personatestuser.org/