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

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https://hg.mozilla.org/integration/gaia-central/rev/6a21440c4b11
Author: steveck-chung <schung@mozilla.com>
Desc: Merge pull request #20417 from steveck-chung/bug-1021788

Bug 1021788 - [Messages] Can't click on the suggestion list when there are a lot of recipients in the recipients panel. r=julienw

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https://hg.mozilla.org/integration/gaia-central/rev/78a211078c39
Author: Steve Chung <schung@mozilla.com>
Desc: Bug 1021788 - [Messages] Can't click on the suggestion list when there are a lot of recipients in the recipients panel
Bumping manifests a=b2g-bump