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

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https://hg.mozilla.org/integration/gaia-central/rev/4cd15b46b87a
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #13605 from bzbarsky/master

Bug 937474.  Get rid of cloneNode() with no arguments in Gaia code.  r=s...

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https://hg.mozilla.org/integration/gaia-central/rev/2fe12f66abb0
Author: Boris Zbarsky <bzbarsky@mit.edu>
Desc: Bug 937474.  Get rid of cloneNode() with no arguments in Gaia code.  r=sicking