Fixed wording for formatting integers: precision is not allowed.

Doc/library/string.rst

@@ -395,7 +395,7 @@ displayed after the decimal point for a floating point value formatted with
 ``'f'`` and ``'F'``, or before and after the decimal point for a floating point
 value formatted with ``'g'`` or ``'G'``.  For non-number types the field
 indicates the maximum field size - in other words, how many characters will be
-used from the field content. The *precision* is ignored for integer values.
+used from the field content. The *precision* is not allowed for integer values.
 
 Finally, the *type* determines how the data should be presented.