Bump scalatest version in tests/test-cross
Bump scalatest version in tests/test-cross

The travis build has been failing with issues with the scalatest 3.0.5
jar so let's try with 3.0.6.

mdedetrich/sbt,xuwei-k/xsbt,mdedetrich/sbt,xuwei-k/xsbt,mdedetrich/sbt,xuwei-k/xsbt,xuwei-k/xsbt,sbt/sbt,xuwei-k/xsbt,sbt/sbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,mdedetrich/sbt