add license （sofastack#515)

tracer-core/src/main/java/com/alipay/common/tracer/core/async/SofaTraceExecutor.java

@@ -1,3 +1,19 @@
+/*
+ * 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.alipay.common.tracer.core.async;
 
 import java.util.concurrent.Executor;
@@ -22,8 +38,8 @@ public SofaTraceExecutor(Executor delegate) {
      *
      * @param command the runnable task
      * @throws RejectedExecutionException if this task cannot be
-     * accepted for execution
-     * @throws NullPointerException if command is null
+     *                                    accepted for execution
+     * @throws NullPointerException       if command is null
      */
     @Override
     public void execute(Runnable command) {