modify readme copyright

Author: 任庆友

README.md

@@ -34,7 +34,7 @@ SensorsAnalytics SDK 是国内第一家开源商用版用户行为采集 SDK，
 
 ## License
 
-Copyright 2015－2020 Sensors Data Inc.
+Copyright 2015－2021 Sensors Data Inc.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.