Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/108f72023349
Author: Dale Harvey <dale@arandomurl.com>
Desc: Bug 997521 - Add prepopulated topsites and history. r=benfrancis

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https://hg.mozilla.org/integration/gaia-central/rev/b360d4538f20
Author: ochameau <poirot.alex@gmail.com>
Desc: Merge pull request #18423 from ochameau/kbd

Bug 996528 - Revive gaia keyboard in firefox nightly. r=vingtetun

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https://hg.mozilla.org/integration/gaia-central/rev/3ff920d13883
Author: Alexandre Poirot <poirot.alex@gmail.com>
Desc: Bug 996528 - Revive gaia keyboard in firefox nightly. r=vingtetun
Bumping manifests a=b2g-bump