Fix comment in 'HashSet' 'size'

Author: rockbmb

Data/HashSet/Base.hs

@@ -241,7 +241,7 @@ null :: HashSet a -> Bool
 null = H.null . asMap
 {-# INLINE null #-}
 
--- | /O(n)/ Return the number of elements in this set.
+-- | /O(1)/ Return the number of elements in this set.
 size :: HashSet a -> Int
 size = H.size . asMap
 {-# INLINE size #-}