Update scala-compiler, scala-library to 2.12.21 (#113)

Author: scala-steward

build.sbt

@@ -2,7 +2,7 @@ organization := "com.lightbend"
 version := "0.0.1"
 name := "cloc-plugin"
 scalaVersion := crossScalaVersions.value.head
-crossScalaVersions := Seq("2.12.20", "2.13.18")
+crossScalaVersions := Seq("2.12.21", "2.13.18")
 crossVersion := CrossVersion.patch
 libraryDependencies +=
   "org.scala-lang" % "scala-compiler" % scalaVersion.value % "provided"