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

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https://hg.mozilla.org/integration/gaia-central/rev/a6b9ea5a0d43
Author: Fernando Jiménez Moreno <ferjmoreno@gmail.com>
Desc: Merge pull request #15463 from ferjm/bug952063.fxa.events

Bug 952063 - Trigger FxAccountsIACHelper 'onlogin', 'onverified' an...

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https://hg.mozilla.org/integration/gaia-central/rev/eaebd0f78174
Author: Fernando Jiménez <ferjmoreno@gmail.com>
Desc: Bug 952063 - Trigger FxAccountsIACHelper 'onlogin', 'onloginverified' and 'onlogout' events when required. r=alive

Address Alive review comments
Bumping manifests a=b2g-bump