Use the executable "nodejs" 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).
By default, it looks for an executable called `"node"`, but on
the community build infrastructure, Node.js is called `"nodejs"`.
This commit instructs Scala.js to use `"nodejs"` instead.

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",
+        // - Use Node.js with the executable "nodejs" instead of "node" (environmental in the CI infrastructure)
+        "set jsEnv in testSuite := NodeJSEnv(executable = \"nodejs\").value"
       ]
     }
   }