HugeGrap-499: fix english grammer in lock

Change-Id: I36c123eb7dfb101f99a176fcd9b2ee1f0f0211d7
Signed-off-by: Liu Jie <liujie23@baidu.com>

src/main/java/com/baidu/hugegraph/concurrent/Lock.java

@@ -1,10 +1,26 @@
+/*
+ * Copyright 2017 HugeGraph Authors
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with this
+ * work for additional information regarding copyright ownership. The ASF
+ * licenses this file to You under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+
 package com.baidu.hugegraph.concurrent;
 
 import java.util.concurrent.atomic.AtomicReference;
 
-/**
- * Created by zhangyi51 on 17/7/20.
- */
 public class Lock {
 
     private String name;
@@ -24,8 +40,8 @@ public class Lock {
         Thread current = Thread.currentThread();
         if (!this.sign.compareAndSet(current, null)) {
             throw new RuntimeException(String.format(
-                      "Thread '%s' try to unlock '%s' " +
-                      "which is held by other thread now.",
+                      "Thread '%s' trying to unlock '%s' " +
+                      "which is held by other threads now.",
                       current.getName(), this.name));
         }
     }