build: Use SPDX license expression in package metadata

Fixes #317.

Author: davidparsson

setup.py

@@ -62,7 +62,8 @@ def read_injector_variable(name):
     description=description,
     long_description=long_description,
     long_description_content_type='text/markdown',
-    license='BSD',
+    license_expression='BSD-3-Clause',
+    license_files=['COPYING'],
     platforms=['any'],
     packages=['injector'],
     package_data={'injector': ['py.typed']},