Inconsistent parens behaviour on TypeSpecs when formatting.

[seivan]

Environment

• Elixir & Erlang versions (elixir --version):

  
  Erlang/OTP 20 [erts-9.3] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]

Elixir 1.6.4 (compiled with OTP 20)

* Operating system: 

macOS High Sierra 10.13.3 (17D102)

### Current behavior

Formatter assigns parens to typespecs in an inconsistent manner. My guess is it makes no distinction between functions and typespec and if something looks like a function it gets parens. 
```elixir
  @spec new(Point.t, Size.t) :: t

becomes

  @spec new(Point.t(), Size.t()) :: t

Expected behavior

Either don't add parens at all to specs (my preference!) or be consistent

  @spec new(Point.t, Size.t) :: t

or

  @spec new(Point.t(), Size.t()) :: t()

[josevalim]

Duplicate of #7401. :) --

José Valimwww.plataformatec.com.br http://www.plataformatec.com.br/Founder and Director of R&D

[seivan]

This answers the question https://github.com/elixir-lang/elixir/issues/7401#issuecomment-368804268