Allow Scala binary (short form) version as Scala version

Short form (`2.10`, `2.11` or `2.12`) will be allowed as `scalaVersion` configuration parameter value.

E.g. both `2.11` and `2.11.8` will be accepted and mapped to `scalac-scoverage-plugin_2.11` and `scalac-scoverage-runtime_2.11` artifacts used internally.