Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/ad7cdef5754a
Author: Jonathan Griffin <jgriffin@mozilla.com>
Desc: Bug 965882 - Re-land 5a0f5ee71152e7f365bf078e345422bb2b1fef7c now that related infrastructure problems have been addressed, r=ahal
Bumping manifests a=b2g-bump