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

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https://hg.mozilla.org/integration/gaia-2_0/rev/71c4c740f979
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Revert "Bug 1019546 - [Visual Refresh][Dialer] Fix dial pad and contacts overlapping when being switched between. r=rik"

This reverts commit dd3b9f32a60746366c8b6b5118fa2a556e5d73a9.
Bumping manifests a=b2g-bump