docs: fix simple typo, expections -> exception

There is a small typo in test/html_validator.py.

Should read `exception` rather than `expections`.

Author: timgates42

test/html_validator.py

@@ -14,5 +14,5 @@ def handle_starttag(self, tag, attrs):
 def assertValidHTML(text):
     h = SimpleParser()
     h.feed(text) 
-    # throws expections if invalid.
+    # throws exception if invalid.
     return True