Relax dependency on typing-extensions (#284)

Author: gazorby

setup.cfg

@@ -36,7 +36,7 @@ include_package_data = True
 
 install_requires =
   pytest >= 6.1.0
-  typing-extensions >= 4.0; python_version < "3.8"
+  typing-extensions >= 3.7.2; python_version < "3.8"
 
 [options.extras_require]
 testing =