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

========

https://hg.mozilla.org/integration/gaia-central/rev/2d81ea943bc1
Author: Mihai Cîrlănaru <mihai@cirlanaru.com>
Desc: Merge pull request #13726 from mihai/bug_937970

Bug 937970 - [Settings] Move 'Sample Format' section below language...

========

https://hg.mozilla.org/integration/gaia-central/rev/7e3a76a2cf94
Author: Mihai Cirlanaru <mihai@cirlanaru.com>
Desc: Bug 937970 - [Settings] Move 'Sample Format' section below language selector. r=arthurcc