Bumping gaia.json for 1 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/1607c58d20be
Author: Corey Frang <gnarf37@gmail.com>
Desc: Bug 935710 - [Settings][Tests] Write unit tests for mvvm - r=arthurcc

- Adds unit tests for mvvm/ code
- Corrects some implementation errors in mvvm
- Fixes jshint for mvvm code

Closes gh-13442