Update sbt-scalajs-crossproject to 1.2.0 (#450)

Author: scala-steward

project/plugins.sbt

@@ -1,5 +1,5 @@
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % "1.8.0")
-addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "1.1.0")
+addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "1.2.0")
 addSbtPlugin("com.github.sbt" % "sbt-ci-release" % "1.5.10")
 
 addSbtPlugin("org.scalameta" % "sbt-scalafmt" % "2.4.6")