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

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https://hg.mozilla.org/integration/gaia-central/rev/c6b957defd1f
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #16658 from KevinGrandon/bug_974918_use_content_scripts

Bug 974918 - Update marionette content scripts version to 0.0.4

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https://hg.mozilla.org/integration/gaia-central/rev/713d61db2f74
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 974918 - Update marionette content scripts version to 0.0.4
Bumping manifests a=b2g-bump