Edge dependencies

[ged]

concurrent-ruby-edge depends on concurrent-ruby with a version specification of ~> 1.2.0, which means that it can't be used with 1.3.1. If we're using classes from -edge should we really stick to 1.2.x of the other two libraries? Are there plans to update -edge so it works with newer versions of the main two libraries? I couldn't find any discussion of it in the changelog or issues, but I might have overlooked something.

[eregon]

Thanks for the report, let's discuss this in #1052 as it's more visible.