update-third-party: Add license notice

Our Git infrastructure scripts use the "Apache License 2.0".

Utilities/Scripts/update-third-party.bash

@@ -1,3 +1,19 @@
+#=============================================================================
+# Copyright 2015-2016 Kitware, Inc.
+#
+# 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.
+#=============================================================================
+
 ########################################################################
 # Script for updating third party packages.
 #