v3.1.1

A deployment error meant that v3.1.0 wasn't released, these release notes cover it as well.

Fixed

• Fix stdin detection for output redirection #750 (@lox)

Changed

• Add ubuntu docker image #749 (@lox)
• Support --no-interpolation option in pipeline upload #733 (@lox)
• Bump our Docker image base to alpine v3.7 #745 (@sj26)
• Better error for multiple file args to artifact upload #740 (@toolmantim)