bump mima version, to work with sbt 1.3

Author: SethTisue

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)