Use proper SPDX identifier

Author: Maximilian Wirtz

setup.cfg

@@ -7,7 +7,7 @@ long_description_content_type = text/x-rst
 url = https://uritemplate.readthedocs.org
 author = Ian Stapleton Cordasco
 author_email = graffatcolmingov@gmail.com
-license = BSD 3-Clause License or Apache License, Version 2.0
+license = BSD 3-Clause OR Apache-2.0
 license_file = LICENSE
 classifiers =
     Development Status :: 5 - Production/Stable