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

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https://hg.mozilla.org/integration/gaia-central/rev/85bebb37650e
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #16375 from julienw/bump-test-agent-0.18.0

Bug 973665 - Bump version to 0.18.0 in Gaia r=me

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https://hg.mozilla.org/integration/gaia-central/rev/c7e27df3a616
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 973665 - Bump version to 0.18.0 in Gaia
Bumping manifests a=b2g-bump