bump Scala 2.12.4 -> 2.12.6

Author: SethTisue

build.sbt

@@ -7,7 +7,7 @@ name    := "scala-partest"
 version := "1.1.4-SNAPSHOT"
 
 scalaVersionsByJvm in ThisBuild := {
-  val vs = List("2.12.4", "2.13.0-M3")
+  val vs = List("2.12.6", "2.13.0-M3")
 
   Map(
     8 -> vs.map(_ -> true),