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

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https://hg.mozilla.org/integration/gaia-central/rev/5cd2ec7bea21
Author: Zac <zcampbell@mozilla.com>
Desc: Revert "Revert "Bug 936703 - [async_storage] callback in transaction.oncomplete event. r=djf""

This reverts commit 98dee6b94048556b02a3f9950b7bfe2053c85e77.
Bumping manifests a=b2g-bump