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

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https://hg.mozilla.org/integration/gaia-central/rev/a8a0fd61079b
Author: Ed Morley <emorley@mozilla.com>
Desc: Revert "Bug 990035 - Modify phone-sized tutorial to show vertical-scroll, notifications & sheets video" for intermittent failures in tutorial_test.js

This reverts commit fabeaffcc637780a490cfcca023aa33ee42041f4.
Bumping manifests a=b2g-bump