Uses better random generator

Author: lukaszlenart

core/src/main/java/org/apache/struts2/util/TokenHelper.java

@@ -27,6 +27,7 @@
 import com.opensymphony.xwork2.util.logging.LoggerFactory;
 
 import java.math.BigInteger;
+import java.security.SecureRandom;
 import java.util.Map;
 import java.util.Random;
 
@@ -51,7 +52,7 @@ public class TokenHelper {
      */
     public static final String TOKEN_NAME_FIELD = "struts.token.name";
     private static final Logger LOG = LoggerFactory.getLogger(TokenHelper.class);
-    private static final Random RANDOM = new Random();
+    private static final Random RANDOM = new SecureRandom();
 
 
     /**