com.opensymphony.module.sitemesh.Factory no longer works with Java 11

resolves sitemesh#36

src/main/java/com/opensymphony/module/sitemesh/Factory.java

@@ -30,7 +30,6 @@
 import java.lang.reflect.InvocationTargetException;
 
 import javax.naming.InitialContext;
-import javax.rmi.PortableRemoteObject;
 
 /**
  * Factory responsible for creating appropriate instances of implementations. This is specific to a web context and is
@@ -114,9 +113,8 @@ private static String getEnvEntry(String envEntry, String defaultValue) {
             if (Container.get() != Container.JRUN) {
                 // TODO: JRun really isn't happy with this
                 InitialContext ctx = new InitialContext();
-                Object o = ctx.lookup("java:comp/env/" + envEntry);
+                result = (String) ctx.lookup("java:comp/env/" + envEntry);
                 ctx.close();
-                result = (String) PortableRemoteObject.narrow(o, String.class); // rmi-iiop friendly.
             }
         } catch (Exception | NoClassDefFoundError e) {
             // failed - don't moan, just return default.