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

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https://hg.mozilla.org/integration/gaia-central/rev/9e676b86fff8
Author: Martijn <martijn.martijn@gmail.com>
Desc: Merge pull request #26855 from JohanLorenzo/bug-926881

Bug 926881 - Write test to enable USB storage

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https://hg.mozilla.org/integration/gaia-central/rev/528042f4a2d6
Author: Johan Lorenzo <jlorenzo@mozilla.com>
Desc: Bug 926881 - Write test to enable USB storage
Bumping manifests a=b2g-bump