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

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https://hg.mozilla.org/integration/gaia-central/rev/6b7becdde98b
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #19855 from KevinGrandon/bug_1018701_move_media_samples

Bug 1018701 - Move media-samples folder into test_media

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https://hg.mozilla.org/integration/gaia-central/rev/96175cda706f
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1018701 - Move media-samples folder into test_media r=yurenju
Bumping manifests a=b2g-bump