Make spec clearer for update functions in Map (#10223)
Make spec clearer for update functions in Map (#10223)

* It removes the concept of the "get" value
* Renames "initial" argument to "default"
* Makes use of the concept of "current value" which was already present in some
  functions, and uses this in the examples and the specs consistently

kimshrier/elixir,pedrosnk/elixir,kimshrier/elixir,kelvinst/elixir,pedrosnk/elixir,joshprice/elixir,ggcampinho/elixir,kelvinst/elixir,ggcampinho/elixir,michalmuskala/elixir,elixir-lang/elixir