use Scala 2.13.x mainly

Author: tsuyoshizawa

build.sbt

@@ -11,8 +11,8 @@ lazy val scalaOAuth2ProviderSettings =
   Defaults.coreDefaultSettings ++
     Seq(
       organization := "com.nulab-inc",
-      scalaVersion := "2.12.8",
-      crossScalaVersions := Seq("2.12.8", "2.11.12", "2.13.0"),
+      scalaVersion := "2.13.0",
+      crossScalaVersions := Seq("2.13.0", "2.12.8", "2.11.12"),
       scalacOptions ++= Seq("-deprecation", "-unchecked", "-feature"),
       scalacOptions ++= unusedWarnings,
       publishTo := {