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

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https://hg.mozilla.org/integration/gaia-central/rev/676a2478d117
Author: Albert <acperez@tid.es>
Desc: Merge pull request #13591 from acperez/bug-937067

Bug 937067 - Add compatibility with new async method availableNetworks of NetworkStats API. r=salva

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https://hg.mozilla.org/integration/gaia-central/rev/30b2beb55cfe
Author: Albert <acperez@tid.es>
Desc: Bug 937067 - Add compatibility with new async method availableNetworks of NetworkStats API. r=salva