Fix a spelling error.

pep-0362.txt

@@ -320,7 +320,7 @@ Annotation Checker
                                          format(func=sig.qualname, arg=param.name))
 
         def check_type(sig, arg_name, arg_type, arg_value):
-            # Internal function that incapsulates arguments type checking
+            # Internal function that encapsulates arguments type checking
             if not isinstance(arg_value, arg_type):
                 raise ValueError("{func}: wrong type of {arg!r} argument, " \
                                  "{exp!r} expected, got {got!r}". \