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

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https://hg.mozilla.org/integration/gaia-central/rev/96ec594716c9
Author: Rex KM Lee <rexboy@mozilla.com>
Desc: Merge pull request #13615 from rexboy7/fix-bug923646

Bug 923646 - add duration to conference call

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https://hg.mozilla.org/integration/gaia-central/rev/59dd4ffb22b1
Author: Rex Lee <rexboy@mozilla.com>
Desc: Bug 923646 - add duration to conference call