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

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https://hg.mozilla.org/integration/gaia-central/rev/958f5e5dff3d
Author: dwi2 <dwi2@dwi2.com>
Desc: Merge pull request #14797 from dwi2/bug937561

Bug 937561 - get both available network list and known network list, and...

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https://hg.mozilla.org/integration/gaia-central/rev/19311815168b
Author: tzhuang <tzhuang@mozilla.com>
Desc: Bug 937561 - get both available network list and known network list, and make union of them to present to settings app