Python 3.9 required

setup.py

@@ -25,9 +25,5 @@ setup(
             'gsuitesync=gsuitesync:main',
         ]
     },
-    extras_require={
-        ':python_version < "3.7"': [
-            'dataclasses',
-        ],
-    }
+    python_requires='>=3.9',
 )