Fixes #1201. Display instruction to overrideScalaVersion

Fixes #1201

scala-library is currently treated as just one of the library modules. This means that it’s at the mercy of eviction if some other library uses newer version of scala-library.

This PR displays the instruction on how to force `scalaVersion` if `warnScalaVersionEviction` flag is true on `EvictionWarningOptions`.

/review @havocp