fix typo in comment (ZConfig.components.logger.formatter)

Co-Authored-By: Jason Madden <jamadden@gmail.com>

ZConfig/components/logger/formatter.py

@@ -250,7 +250,7 @@ def __call__(self):
                 # non-standard, so we reach under the covers a bit.
                 #
                 # Python 3.8 adds a validate option, defaulting to True,
-                # which cases the format string to be checked.  Since
+                # which causes the format string to be checked.  Since
                 # safe-template is not a standard style, we want to
                 # suppress this.
                 #