Explicitly use sbt-scalajs-crossproject.

This will be required for compatibility with Scala.js 1.0.0-M2.

Author: sjrd

build.sbt

@@ -1,3 +1,5 @@
+import sbtcrossproject.crossProject
+
 crossScalaVersions in ThisBuild := Seq("2.12.4", "2.11.12", "2.10.7", "2.13.0-M2")
 scalaVersion in ThisBuild := (crossScalaVersions in ThisBuild).value.head
 
@@ -56,7 +58,7 @@ lazy val root: Project = project.in(file(".")).
     pomIncludeRepository := { _ => false }
   )
 
-lazy val testSuite = crossProject.
+lazy val testSuite = crossProject(JSPlatform, JVMPlatform).
   jsConfigure(_ .enablePlugins(ScalaJSJUnitPlugin)).
   settings(commonSettings: _*).
   settings(

project/build.sbt

@@ -3,4 +3,11 @@ val scalaJSVersion =
 
 addSbtPlugin("org.scala-js" % "sbt-scalajs" % scalaJSVersion)
 
+{
+  if (scalaJSVersion != "1.0.0-M1")
+    addSbtPlugin("org.portable-scala" % "sbt-scalajs-crossproject" % "0.3.0")
+  else
+    Nil
+}
+
 addSbtPlugin("org.scalastyle" % "scalastyle-sbt-plugin" % "0.8.0")