update license year

Author: jkeam

README.md

@@ -156,6 +156,6 @@ client.add_to_many(activity, feeds)
 
 ### Copyright and License Information
 
-Copyright (c) 2014-2018 Stream.io Inc, and individual contributors. All rights reserved.
+Copyright (c) 2014-2020 Stream.io Inc, and individual contributors. All rights reserved.
 
 See the file "LICENSE" for information on the history of this software, terms & conditions for usage, and a DISCLAIMER OF ALL WARRANTIES.