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

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https://hg.mozilla.org/integration/gaia-central/rev/b2839ae38bd3
Author: steveck-chung <schung@mozilla.com>
Desc: Merge pull request #17804 from steveck-chung/message-2.25X-image

Bug 983074 - [MADAI][SMS] @2.25x assets update for SMS. r=borja.

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https://hg.mozilla.org/integration/gaia-central/rev/db94a10c5ee7
Author: Steve Chung <schung@mozilla.com>
Desc: Bug 983074 - [MADAI][SMS] @2.25x assets update for SMS
Bumping manifests a=b2g-bump