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

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https://hg.mozilla.org/integration/gaia-central/rev/68cba47518ba
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #12373 from wanderview/contacts-static-scrollbar

Bug 919692: define contacts scrollbar in index.html

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https://hg.mozilla.org/integration/gaia-central/rev/47ba5adbd985
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 919692: define contacts scrollbar in index.html