Improve consistency of Enum.chunk_while/4 docs
Improve consistency of Enum.chunk_while/4 docs

A previous commit renamed `element` to `chunk` in the
paragraph above.
kimshrier/elixir,kelvinst/elixir,kimshrier/elixir,ggcampinho/elixir,ggcampinho/elixir,michalmuskala/elixir,elixir-lang/elixir,joshprice/elixir,kelvinst/elixir,pedrosnk/elixir,pedrosnk/elixir