I was taking a look at the logs and the jobs are failing 'cause they try to upload the artifacts twice. The reason is that we are cross-building twice, using travis matrix and setting sbt-release#releaseCrossBuildto true. I've opened oncue/knobs#31 to turn it off
the other option is to use the matrix just for Scalaz-Stream version and let SBT to do the Scala cross-build. But it is nice to have separate jobs for the 4 combinations.