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

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https://hg.mozilla.org/integration/gaia-central/rev/e474736e925e
Author: gasolin <gasolin@gmail.com>
Desc: Merge pull request #12424 from gasolin/issue-920042

Bug 920042 - [Flatfish] not minimize appWraper bar while swipe up to hom...r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/9ba8915376c4
Author: gasolin <gasolin@gmail.com>
Desc: Bug 920042 - [Flatfish] not minimize appWraper bar while swipe up to home gesture is enabled