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

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https://hg.mozilla.org/integration/gaia-central/rev/7cf47b57d881
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 923831 - Intermittent failures in test_kill_all, disabling the test until someone can investigate and/or repair the test