Update LICENSE

Copyright reflects update from here:
https://github.com/d3/d3.github.com/blob/master/LICENSE

Author: Taddywarbucks

LICENSE

@@ -271,7 +271,7 @@ SOFTWARE.
 For D3's World 110m  (spot-oa/ui/flow/world-110m.json):
 ========================================================================
 
-Copyright (c) 2014, Michael Bostock
+Copyright (c) 2014-2019, Michael Bostock
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without