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

========

https://hg.mozilla.org/integration/gaia-2_0/rev/bd21a0a7d478
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #22735 from julienw/1051852-use-domcontentloaded

Bug 1051852 - [Messages] use 'DOMContentLoaded' instead of 'load' to ini...
Bumping manifests a=b2g-bump