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

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https://hg.mozilla.org/integration/gaia-central/rev/af00bc781ef2
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #14088 from mikehenrty/bump-marionette-helper

use new marionette helper, adds waitForElementToDisappear

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https://hg.mozilla.org/integration/gaia-central/rev/c4d245fefa05
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: use new marionette helper, adds waitForElementToDisappear