Update typo in Update BYPOS and BYDAY rules PR (#217)

Fix typo in occurrence

ical/types/recur.py

@@ -93,7 +93,7 @@ def __str__(self) -> str:
 
 
     def as_rrule_weekday(self) -> weekday:
-        """Convert the ocurrence to a weekday value."""
+        """Convert the occurrence to a weekday value."""
         wd = RRULE_WEEKDAY[self.weekday]
         if self.occurrence is None:
             return wd