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

========

https://hg.mozilla.org/integration/gaia-central/rev/b53d2b2064fe
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #15182 from mikehenrty/bug-957769-scanning

Bug 957769 - dont allow multiple scans, r=fcampo

========

https://hg.mozilla.org/integration/gaia-central/rev/bff6382c9e6c
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 957769 - dont allow multiple scans