minor bug in http://www.w3.org/TR/CSS21/grammar.html

Hi.

There is a small bug in the URL in the subject:
`The two occurrences of "\377"...`


There is only one occurrence of \377.

There were two occurences in a previous version of the grammar, where 
the rule for `escape` was:
     {unicode}|\\[ -~\200-\377]
instead of
     {unicode}|\\[^\r\n\f0-9a-f]



Manlio Perillo