Updated pytest minimum required version.

Author: hramezani

setup.py

@@ -28,7 +28,7 @@
 
 tests_require = [
     "pytest>=4.6,<5.0; python_version < '3.5'",
-    "pytest; python_version >= '3.5'",
+    "pytest>=4.6; python_version >= '3.5'",
     "coverage >= 3.7.1, < 5.0.0",
     "pytest-cov",
     "pytest-localserver",