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

========

https://hg.mozilla.org/integration/gaia-2_0/rev/f38ff5e0ce4c
Author: Ghislain 'Aus' Lacroix <aus@noiseport.org>
Desc: Merge pull request #20381 from nullaus/v2.0

Merge pull request #19299 from nullaus/bug982295-browser-api

========

https://hg.mozilla.org/integration/gaia-2_0/rev/b284c81c45a8
Author: Ghislain 'Aus' Lacroix <aus@noiseport.org>
Desc: Merge pull request #19299 from nullaus/bug982295-browser-api

bug 982295 - Use new Browser API download method. r=benfrancis(cherry picked from commit 901646a3279c66daa7621bebb62641779d8ae22c)
Bumping manifests a=b2g-bump