Fix block start pattern

[erszcz]

Hey,

Thanks for maintaining great support for Vim!

This PR fixes a somewhat annoying indentation issue that surfaced with:

Wallaby.Browser.fill_in(some_input_box, with: "some text")

The regex pattern used to discover a block when it spotted a with. This lead to the following code:

defmodule Broken do
  def test do
    f(:arg1, with: :arg2)
  end # ...when we hit Enter/Return here...
end

Being improperly indented:

defmodule Broken do
  def test do
    f(:arg1, with: :arg2)
      end
end

The more withs, the merrier:

defmodule Broken do
  def test do
    f(:arg1, with: :arg2)
    |> g(with: :arg3)
  end

      def test2 do # with 2 `with`s this line got indented like this

  end
end

This commit uses a negative lookahead to make sure the block start pattern only matches if the keyword is not immediately followed by a : colon character.

[sodapopcan]

Oh thank you for this! This actually gives me an idea of what is causing some other indentation issues 🤔

[sodapopcan]

Oh man, I just ran into this... this is exactly what has been causing this super-annoying indentation problem all this time! Thanks again!!!!

[erszcz]

I'm glad I could help! Thanks again for a great plugin!