Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/602ee2a680a0
Author: Doug Sherk <github@sherk.me>
Desc: Revert "Bug 1077331 - Only seek ringtone back to start on ringtone if the file is loaded fully enough to seek. r=etienne"

This reverts commit 815211451d4352ecd4bdda4ae1bad1e0f3f9f2cc.
Bumping manifests a=b2g-bump