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

========

https://hg.mozilla.org/integration/gaia-central/rev/4cdfe9307db3
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Merge pull request #12813 from gabrielesvelto/bug-922574-pressed-button-image

Bug 922574 - Added a pressed state to the switch-calls button r=etienne

========

https://hg.mozilla.org/integration/gaia-central/rev/3a06cb2437c4
Author: Gabriele Svelto <gabriele.svelto@gmail.com>
Desc: Bug 922574 - Added a pressed state to the switch-calls button r=etienne