Making a univeral wheel that supports both Python 2 and 3.

setup.cfg

@@ -1,2 +1,5 @@
 [metadata]
 description-file=README.md
+
+[bdist_wheel]
+universal=1

setup.py

@@ -27,9 +27,9 @@ setup(
             'borgmatic = borgmatic.command:main',
         ]
     },
-    obsoletes=(
+    obsoletes=[
         'atticmatic',
-    ),
+    ],
     tests_require=(
         'flexmock',
         'pytest',