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

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https://hg.mozilla.org/integration/gaia-central/rev/55b9db75de18
Author: Wilson Page <wilsonpage@me.com>
Desc: Merge pull request #19765 from wilsonpage/1008187

Bug 1008187 - [Camera] Update to use <gaia-header>

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https://hg.mozilla.org/integration/gaia-central/rev/882809b3db03
Author: Wilson Page <wilsonpage@me.com>
Desc: Bug 1008187 - [Camera] Update to use <gaia-header>

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https://hg.mozilla.org/integration/gaia-central/rev/7dcb200002dc
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 1013294 - Use the deviceRoot as provided by mozdevice. r=bsilverberg
Bumping manifests a=b2g-bump