Version bump to 1.3.9 to avoid versioning conflicts with 1.3.8

Hi,

during my latest upgrade to Scala 2.11, several incompatibilities showed up.
The last available ScalaBuff version was 1.3.8. - Acc. to github, this version should already include Scala 2.11 support through an additional compiler paramter ("--target=<scala-version").

This, however, did not work because the build drew the ScalaBuff Compiler/Runtime artifacts from a repository (probably Typesafe Release/Snapshot), which is hosting an older flavor of ScalaBuff 1.3.8.

In short: this PR simply bumps up the version to 1.3.9, because 1.3.8 seems to be ambiguous (2 flavors - with and without "--target" parameter).

Also, I removed the Scala 2.9 crossbuild-support because of compilation issues during cross-building. - Scala 2.9 does not have support for string interpolation (s"..") yet.

cheers,
-Tom