Rename the setter functions

[sajidanower23]

In the module Lets.Lens, there is a setter function and a type alias that goes with it.

type Set s t a b =
  (a -> Identity b)
  -> s
  -> Identity t

-- | Let's write an inverse to @over@ that does the @Identity@ wrapping &
-- unwrapping.
sets ::
  ((a -> b) -> s -> t)
  -> ( a -> Identity b)
  -> s
  -> Identity t
  -- -> Set s t a b
sets f idM = Identity . f (getIdentity . idM)

mapped ::
  Functor f =>
  Set (f a) (f b) a b
mapped = sets fmap

set ::
  Set s t a b
  -> s
  -> b
  -> t
set q s b = over q (const b) s

Later in the module, we can see the use of the data structure Set, which has nothing to do with the setter functions and therefore can be confusing.
It may be worth renaming the setter functions, perhaps to update or something else.