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

========

https://hg.mozilla.org/integration/gaia-central/rev/a521b981daaf
Author: Zibi Braniecki <zbigniew.braniecki@gmail.com>
Desc: Merge pull request #25637 from zbraniecki/1091113-improve-l10n-merge

Bug 1091113 - Don't merge obsolete entity fields. r=stas

========

https://hg.mozilla.org/integration/gaia-central/rev/3ec295da54c8
Author: Zibi Braniecki <gandalf@mozilla.com>
Desc: Bug 1091113 - Don't merge obsolete entity fields
Bumping manifests a=b2g-bump