ZOOKEEPER-4494: Fix error message format

cc maoling eolivelli

Author: tison <wander4096@gmail.com>

Reviewers: maoling <maoling@apache.org>

Closes #1838 from tisonkun/patch-2

zookeeper-server/src/main/java/org/apache/zookeeper/server/util/SerializeUtils.java

@@ -101,7 +101,7 @@ public class SerializeUtils {
             txn = new MultiTxn();
             break;
         default:
-            throw new IOException("Unsupported Txn with type=%d" + hdr.getType());
+            throw new IOException("Unsupported Txn with type=" + hdr.getType());
         }
         if (txn != null) {
             try {