Fix inaccurate and badly formatted docs for update

Previously the docs suggested that the update function received the key
as well as the value, but actually it only gets the value.

Author: Dretch

Data/HashMap/Base.hs

@@ -1126,9 +1126,9 @@ adjust# f k0 m0 = go h0 k0 0 m0
         | otherwise = t
 {-# INLINABLE adjust# #-}
 
--- | /O(log n)/  The expression (@'update' f k map@) updates the value @x@ at @k@,
--- (if it is in the map). If (f k x) is @'Nothing', the element is deleted.
--- If it is (@'Just' y), the key k is bound to the new value y.
+-- | /O(log n)/  The expression (@'update' f k map@) updates the value @x@ at @k@
+-- (if it is in the map). If (@f x@) is @'Nothing'@, the element is deleted.
+-- If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
 update :: (Eq k, Hashable k) => (a -> Maybe a) -> k -> HashMap k a -> HashMap k a
 update f = alter (>>= f)
 {-# INLINABLE update #-}

Data/HashMap/Strict/Base.hs

@@ -244,9 +244,9 @@ adjust f k0 m0 = go h0 k0 0 m0
         | otherwise = t
 {-# INLINABLE adjust #-}
 
--- | /O(log n)/  The expression (@'update' f k map@) updates the value @x@ at @k@,
--- (if it is in the map). If (f k x) is @'Nothing', the element is deleted.
--- If it is (@'Just' y), the key k is bound to the new value y.
+-- | /O(log n)/  The expression (@'update' f k map@) updates the value @x@ at @k@
+-- (if it is in the map). If (@f x@) is @'Nothing'@, the element is deleted.
+-- If it is (@'Just' y@), the key @k@ is bound to the new value @y@.
 update :: (Eq k, Hashable k) => (a -> Maybe a) -> k -> HashMap k a -> HashMap k a
 update f = alter (>>= f)
 {-# INLINABLE update #-}