Documentation fix.

Doc/library/ast.rst

@@ -258,5 +258,5 @@ and classes for traversing abstract syntax trees:
    debugging purposes.  The returned string will show the names and the values
    for fields.  This makes the code impossible to evaluate, so if evaluation is
    wanted *annotate_fields* must be set to False.  Attributes such as line
-   numbers and column offsets are dumped by default.  If this is wanted,
+   numbers and column offsets are not dumped by default.  If this is wanted,
    *include_attributes* can be set to ``True``.