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

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https://hg.mozilla.org/integration/gaia-central/rev/5aca6284801d
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #12800 from gaye/bump-marionette-apps

Bump marionette-apps to ~0.3.1 r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/c26bdfdef8e9
Author: Gareth Aye <gaye@mozilla.com>
Desc: Bump marionette-apps to ~0.3.1