Revert to Scala 2.12.20

Author: thesamet

build.sbt

@@ -6,7 +6,7 @@ scalacOptions := Seq("-deprecation", "-unchecked", "-Xlint", "-Yno-adapted-args"
 
 scalacOptions += "-release:8"
 
-scalaVersion := "2.13.16"
+scalaVersion := "2.12.20"
 
 addSbtPlugin("org.portable-scala" % "sbt-platform-deps" % "1.0.1")