Updated nashorn to use ECMA6

src/main/java/noppes/npcs/controllers/ScriptContainer.java

@@ -209,6 +209,9 @@ public class ScriptContainer {
     public void setEngine(String scriptLanguage) {
         if(currentScriptLanguage != null && currentScriptLanguage.equals(scriptLanguage))
             return;
+        if (scriptLanguage.equals("ECMAScript")) {
+            System.setProperty("nashorn.args", "--language=es6");
+        }
         engine = ScriptController.Instance.getEngineByName(scriptLanguage.toLowerCase());
         currentScriptLanguage = scriptLanguage;
     }