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

========

https://hg.mozilla.org/integration/gaia-central/rev/63d9d160359f
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #12938 from vingtetun/hover

Bug 921824 - Highlight color is often not visible after a click on an el...

========

https://hg.mozilla.org/integration/gaia-central/rev/131e102ae349
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 921824 - Highlight color is often not visible after a click on an element. r=arnau