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

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https://hg.mozilla.org/integration/gaia-central/rev/6cea8070de7b
Author: Albert <acperez@tid.es>
Desc: Merge pull request #18417 from acperez/bug-995900

Bug 995900 - build process for operatorvariant app

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https://hg.mozilla.org/integration/gaia-central/rev/63c31d6e44c8
Author: Albert <acperez@tid.es>
Desc: Bug 995900 - build process for operatorvariant app
Bumping manifests a=b2g-bump