Fix old py3 versions

Author: jamesls

requirements.txt

@@ -1,8 +1,8 @@
 wheel==0.24.0
-pytest==6.2.5 ; python_version > '3.4'
-pytest<5.0 ; python_version < '3.0'
-pytest-cov==3.0.0 ; python_version > '3.4'
-pytest-cov<3.0.0 ; python_version < '3.0'
+pytest==6.2.5 ; python_version >= '3.6'
+pytest<5.0 ; python_version < '3.6'
+pytest-cov==3.0.0 ; python_version >= '3.6'
+pytest-cov<3.0.0 ; python_version < '3.6'
 hypothesis==3.1.0 ; python_version < '3.8'
 hypothesis==5.5.4 ; python_version == '3.8'
 hypothesis==5.35.4 ; python_version == '3.9'