Update LICENSE

Add copyright notice

LICENSE

@@ -1,3 +1,17 @@
+Copyright 2013 Mixpanel, Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this work except in compliance with the License.
+You may obtain a copy of the License below, or 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.
+
                                  Apache License
                            Version 2.0, January 2004
                         http://www.apache.org/licenses/