Shut up another serialVersionUID warning

src/main/java/org/sablecc/sablecc/ConflictException.java

@@ -10,6 +10,7 @@ package org.sablecc.sablecc;
 import org.sablecc.sablecc.node.*;
 import java.util.Set;
 
+@SuppressWarnings("serial")
 public class ConflictException extends Exception
 {
   private Set conflictualProductions;