oss: Remove Date Ranges from Copyright in READMEs

Problem/Solution:

The copyright lines in the project README files,
do not need to be date ranges but can simply be
the original (first) year the code was copyrighted.

JIRA Issues: CSL-10588

Differential Revision: https://phabricator.twitter.biz/D613522

README.md

@@ -48,6 +48,6 @@ for more details about how to contribute.
 
 ## License
 
-Copyright 2013-2021 Twitter, Inc.
+Copyright 2013 Twitter, Inc.
 
 Licensed under the Apache License, Version 2.0: https://www.apache.org/licenses/LICENSE-2.0