updated cross build to 2.11.2 and removed 2.9.x
updated version to avoid conflicts in artifact repos (changes have been made after bump to 1.3.8 without incrementing version)
removed Scala 2.9 from crossbuilds to avoid compilation issues (no string interpolation available in Scala 2.9)
updated docs about supported Scala versions
Merge pull request #86 from thomasschoeftner/master

Version bump to 1.3.9 to avoid versioning conflicts with 1.3.8