Update required pytest version, to avoid transitive "pytest >=4.6" condition not being satisfied

Author: echarrod

setup.py

@@ -43,7 +43,7 @@
         ],
         "dev": [
             "pre-commit==1.17.0",
-            "pytest>=3.6.0",
+            "pytest>=4.6.0",
             "pytest-cov>=2.7.1",
             "pylint==1.9.4",
             "pylint-exit>=1.1.0",