Use unmanagedSources instead of unmanagedSourceDirectories

[olafurpg]

See #331 (comment)

A good place to start looking at this is here

scalafix/scalafix-sbt/src/main/scala/scalafix/sbt/ScalafixPlugin.scala

Line 207 in c0a2698

unmanagedSourceDirectories.all(filter).value.flatten.collect {

The motivation for using unmanagedSourceDirectories was to make the sbt console output pretty when debugging the flags passed to the scalafix-cli. If we do this change, we probably need to minimize the output here

scalafix/scalafix-sbt/src/main/scala/scalafix/sbt/ScalafixPlugin.scala

Line 263 in c0a2698

log.info(s"Running scalafix $nonBaseArgs")