Fix a flake8 warning

Author: tk0miya

sphinx/ext/extlinks.py

@@ -72,7 +72,8 @@ def check_uri(self, refnode: nodes.reference) -> None:
 
         for alias, (base_uri, _caption) in self.app.config.extlinks.items():
             if sys.version_info < (3, 7):
-                # Replace a leading backslash because re.escape() inserts a backslash before % on python 3.6
+                # Replace a leading backslash because re.escape() inserts a backslash before %
+                # on python 3.6
                 uri_pattern = re.compile(re.escape(base_uri).replace('\\%s', '(?P<value>.+)'))
             else:
                 uri_pattern = re.compile(re.escape(base_uri).replace('%s', '(?P<value>.+)'))