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

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https://hg.mozilla.org/integration/gaia-central/rev/8c59f102e8fe
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #17608 from KevinGrandon/bug_988007_compose_styling

Bug 988007 - Unable to place cursor in front of the first character on a line r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/d192dd0118c3
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 988007 - Unable to place cursor in front of the first character on a line r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/7e0333b78df9
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Bug 986173 - Disable the reflow test for now
Bumping manifests a=b2g-bump