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

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https://hg.mozilla.org/integration/gaia-central/rev/6a8abff70cba
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #14609 from arroway/bug-831948

Bug 831948 - WiFi Tethering should default to WPA2

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https://hg.mozilla.org/integration/gaia-central/rev/92c1bc833772
Author: Stephanie Ouillon <arroway@mozilla.com>
Desc: Bug 831948 - WiFi Tethering should default to WPA2

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https://hg.mozilla.org/integration/gaia-central/rev/df288280b57a
Author: Cristian Rodriguez <crdlc@tid.es>
Desc: Merge pull request #14709 from crdlc/bug-950671

Bug 950671 - Detail contacts shows the previous photo contact for a whil...

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https://hg.mozilla.org/integration/gaia-central/rev/81d656eb9fcf
Author: crdlc <crdlc@tid.es>
Desc: Bug 950671 - Detail contacts shows the previous photo contact for a while and the animation is not very synchronized