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

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https://hg.mozilla.org/integration/gaia-central/rev/cb8682316360
Author: Jan Jongboom <janjongboom@gmail.com>
Desc: Merge pull request #16575 from comoyo/revert_new_keyboard_promisify

Revert "Bug 975992 - Keep keyboard2 state in Gecko rather than Gaia"

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https://hg.mozilla.org/integration/gaia-central/rev/531299940f5d
Author: Jan Jongboom <janjongboom@gmail.com>
Desc: Revert "Bug 975992 - Keep keyboard2 state in Gecko rather than Gaia"

This reverts commit 5ffd3aefddeb628ff27405e6d07281b108b5dec9.
Bumping manifests a=b2g-bump