Test: enable Node.js when testing Scala.js.

Scala.js will change its default runner from Rhino to Node.js in
0.6.13 (see scala-js/scala-js#2579).
This commit preemptively tests whether this is going to be a
problem for the community build.

Author: sjrd

common.conf

@@ -547,7 +547,9 @@ build += {
         // - Disable compiler/test because it is very fragile.
         "set test in (Build.compiler, Test) := {}",
         // - Disable fatal Scaladoc warnings, also fragile
-        "removeScalacOptions -Xfatal-warnings"
+        "removeScalacOptions -Xfatal-warnings",
+        // - Test that we can use Node.js for the change of default in Scala.js
+        "set scalaJSUseRhino in Global := false"
       ]
     }
   }