Update scala-library to 2.12.20 (#107)

build.sbt

@@ -42,7 +42,7 @@ lazy val plugin = project.in(file("plugin"))
   .settings(
     name := "sbt-benchdb",
     sbtPlugin := true,
-    scalaVersion := "2.12.19",
+    scalaVersion := "2.12.20",
     buildInfoKeys := Seq[BuildInfoKey](organization, core / name, version, core / scalaVersion),
     buildInfoPackage := "com.lightbend.benchdb.sbtplugin",
     publishMavenStyle := false,