Update sbt to 1.3.3 (was 1.2.8)

also bump sbt-scala-version to get newer mima version,
old mima version doesn't work with sbt 1.3

Author: scala-steward

project/build.properties

@@ -1,2 +1 @@
-# Not 1.3.0 due to https://github.com/sbt/sbt/issues/5043
-sbt.version=1.2.8
+sbt.version=1.3.3

project/plugins.sbt

@@ -1,7 +1,7 @@
 val scalaJSVersion =
   Option(System.getenv("SCALAJS_VERSION")).filter(_.nonEmpty).getOrElse("0.6.29")
 
-addSbtPlugin("org.scala-lang.modules" % "sbt-scala-module" % "2.1.2")
+addSbtPlugin("org.scala-lang.modules" % "sbt-scala-module" % "2.1.3")
 
 addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "0.6.1")
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % scalaJSVersion)