Scalafix's scalahost dependency should depend on scala version

[lolgab]

https://github.com/cvogt/cbt/blob/663a0f9095ab77138a6a8bc76b788dc2b55928b7/plugins/scalafix/build/build.scala#L21

Now the scalahost dependency is fixed but if you set the defaultScalaVersion = "2.12.3" for example the only version on maven is the "1.8.0" Maven central .. For scala 2.12.2 I don't know what is the best way to achieve that... Maybe a Map in the plugin/scalafix/build/build.scala file ... If it is a accepted solution I can submit a PR.

Lorenzo :)