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

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https://hg.mozilla.org/integration/gaia-central/rev/5125209935fa
Author: Jared Hirsch <ohai@6a68.net>
Desc: Merge pull request #18438 from 6a68/bug-996476-hide-accounts-header

Bug 996476 - Hide Accounts section header if fxa preffed off

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https://hg.mozilla.org/integration/gaia-central/rev/a0270e086719
Author: Jared Hirsch <ohai@6a68.net>
Desc: Bug 996476 - Hide Accounts section header if fxa preffed off r=arthurcc
Bumping manifests a=b2g-bump