SPARK-5984: Add info to LICENSE

LICENSE

@@ -771,6 +771,22 @@ 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.
 
+========================================================================
+For TestTimSort (core/src/test/java/org/apache/spark/util/collection/TestTimSort.java):
+========================================================================
+Copyright (C) 2015 Stijn de Gouw
+
+Licensed 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.
 
 ========================================================================
 For LimitedInputStream