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

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https://hg.mozilla.org/integration/gaia-central/rev/c39acb3bccce
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Revert "Bug 1014418 - Dispatching hardware button event in Gaia"

This reverts commit f02c0c64cad956ba18d257f85ef40eb8c634f9e4.
Bumping manifests a=b2g-bump