#782: Adapt setup to use isoduration only above python 3.6

Author: nezhar

setup.cfg

@@ -39,7 +39,7 @@ format =
     strict-rfc3339
     webcolors
     uri_template
-    isoduration
+    isoduration;python_version>'3.6'
 format_nongpl =
     fqdn
     idna
@@ -48,7 +48,7 @@ format_nongpl =
     rfc3986-validator>0.1.0
     rfc3339-validator
     uri_template
-    isoduration
+    isoduration;python_version>'3.6'
 
 [options.entry_points]
 console_scripts =