Plugins: Fix loading of webapp configuration classes

on Jetty 9.4 by whitelisting them as allowed server classes
(ticket #2385)

router/java/src/net/i2p/router/RouterVersion.java

@@ -18,7 +18,7 @@ public class RouterVersion {
     /** deprecated */
     public final static String ID = "Monotone";
     public final static String VERSION = CoreVersion.VERSION;
-    public final static long BUILD = 17;
+    public final static long BUILD = 18;
 
     /** for example "-test" */
     public final static String EXTRA = "-rc";