Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/ac9e11ac7ef1
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #17334 from vingtetun/bug981610.keyboards

Bug 981610 - Remove some CSS warnings on the keyboard app. r=janjongboom

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https://hg.mozilla.org/integration/gaia-central/rev/9eb973a412fc
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 981610 - Remove some CSS warnings on the keyboard app. r=janjongboom

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https://hg.mozilla.org/integration/gaia-central/rev/72858e9f347e
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #17202 from rnowm/981887

Bug 981887 - Update button design using current BB structure and "Plan B" design

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https://hg.mozilla.org/integration/gaia-central/rev/f86b04fd966d
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 981887 - Update button design using current BB structure and "Plan B" design
Bumping manifests a=b2g-bump