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

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https://hg.mozilla.org/integration/gaia-central/rev/6ccba5b64dc7
Author: evanxd <itoyxd@gmail.com>
Desc: Merge pull request #16244 from evanxd/bug-972160

Bug 972160 - Run specific marionette tests for multiple times on Travis.

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https://hg.mozilla.org/integration/gaia-central/rev/56f4cb89a7c6
Author: Evan Xd <itoyxd@gmail.com>
Desc: Bug 972160 - Run specific marionette tests for 30 times on Travis.
Bumping manifests a=b2g-bump