fix(docs): example formatting

Author: hermansje

pythonwhat/check_wrappers.py

@@ -558,7 +558,7 @@ def __init__(self, i):
 
         :Example:
 
-            Suppose you want to verify whether the student did a `try-except` statement properly:
+            Suppose you want to verify whether the student did a `try-except` statement properly: ::
 
                 do_dangerous_thing = lambda n: n