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

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https://hg.mozilla.org/integration/gaia-central/rev/334588c8cd8a
Author: Jan Keromnes <janx@linux.com>
Desc: Merge pull request #18237 from jankeromnes/updatechannel

Bug 984962 - Expose app.update.{channel,url} in the Developer menu. r=21

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https://hg.mozilla.org/integration/gaia-central/rev/787fba14b1d5
Author: Jan Keromnes <janx@linux.com>
Desc: Bug 984962 - Expose app.update.{channel,url} in the Developer menu. r=21
Bumping manifests a=b2g-bump