Update sbt-scalajs, scalajs-compiler to 0.6.31

Author: scala-steward

project/plugins.sbt

@@ -4,7 +4,7 @@ libraryDependencies += "commons-io" % "commons-io" % "2.6"
 
 addSbtPlugin("com.thoughtworks.sbt-scala-js-map" % "sbt-scala-js-map" % "4.0.0")
 
-addSbtPlugin("org.scala-js" % "sbt-scalajs" % "0.6.28")
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % "0.6.31")
 
 addSbtPlugin("org.xerial.sbt" % "sbt-sonatype" % "3.8.1")