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

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https://hg.mozilla.org/integration/gaia-central/rev/336e9464c144
Author: Malini Das <thehyperballad@gmail.com>
Desc: Merge pull request #14476 from malini/mixin

Bug 925398 - Refactor runtests.py to follow Mixin pattern, r=davehunt

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https://hg.mozilla.org/integration/gaia-central/rev/c43202d0bbc9
Author: Malini Das <mdas@mozilla.com>
Desc: Bug 925398 - Refactor runtests.py to follow Mixin pattern