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

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https://hg.mozilla.org/integration/gaia-central/rev/ac1bd42712a6
Author: Malini Das <thehyperballad@gmail.com>
Desc: Merge pull request #14571 from malini/version

Bug 947001 - bump marionette-client and gaiatest versions, r=davehunt

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https://hg.mozilla.org/integration/gaia-central/rev/69618e357429
Author: Malini Das <mdas@mozilla.com>
Desc: bump marionette-client and gaiatest versions, enable gaia-ui-tests