add LICENSE file reference

Author: shunt16

setup.cfg

@@ -1,5 +1,5 @@
 [metadata]
-license-files = LICENSE
+license_files = LICENSE
 
 [versioneer]
 # See the docstring in versioneer.py for instructions. Note that you must

setup.py

@@ -20,6 +20,7 @@ def read(filename):
     name="obsarray",
     url="https://github.com/comet-toolkit/obsarray",
     license="GPLv3",
+    license_files=["LICENSE"],
     author="CoMet Toolkit Team",
     author_email="team@comet-toolkit.org",
     description="Measurement data handling in Python",