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

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https://hg.mozilla.org/integration/gaia-central/rev/896e4c28c82d
Author: russnicoletti <rnicoletti@mozilla.com>
Desc: Merge pull request #18546 from russnicoletti/showPlayer_unit_testing

Bug 979636 - Unit tests for video app -- showPlayer unit tests

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https://hg.mozilla.org/integration/gaia-central/rev/c7fabd4a7e40
Author: Russ Nicoletti <rnicoletti@mozilla.com>
Desc: Bug 979636 - Unit tests for video app -- showPlayer unit tests
Bumping manifests a=b2g-bump