[selectors3] Typo in "Specificity" section

In the "Calculating a selector's specificity" section
(https://drafts.csswg.org/selectors-3/#specificity) there is a note that
reads as follows:

> Note: Repeated occurrances of the same simple selector are allowed and do
increase specificity.

The word "occurrences" is misspelled.

Thanks,
Louis