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

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https://hg.mozilla.org/integration/gaia-central/rev/175b7a89aa5f
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #12982 from wanderview/contacts-webidl-sim

Bug 928954: Fix contact sim import for webidl changes.  r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/f1c802e00fa0
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 928954: Fix contact sim import for webidl changes