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

========

https://hg.mozilla.org/integration/gaia-central/rev/a828864b5d77
Author: gitmai <mri@tid.es>
Desc: Merge pull request #17627 from gitmai/bug-987283-CC-300ms-cold-load-launch

Bug 987283 -usage app cold_load_launch regressed 300ms Mar 22
r=salva

========

https://hg.mozilla.org/integration/gaia-central/rev/320068047e90
Author: mai <mri@tid.es>
Desc: Bug 987283 -usage app cold_load_launch regressed 300ms Mar 22
Bumping manifests a=b2g-bump