Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/a7416333b02d
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1016431 - [System] Fix unit tests with a newer mocha r=alive

========

https://hg.mozilla.org/integration/gaia-central/rev/4d83404ff4c4
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #20691 from zacc/bug_941544

Bug 941544 - running_apps should always switch to System frame before ex...

========

https://hg.mozilla.org/integration/gaia-central/rev/3cf34806a0e1
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 941544 - running_apps should always switch to System frame before executing system javascript
Bumping manifests a=b2g-bump