The Base.request!/1 return value is not wrapped in a ok-tuple

[flambard]

This PR is a fix of the typespec for Base.request!/1. The return value is not supposed to be wrapped in a ok-tuple.

[mjquinlan2000]

For anyone also affected by dialyzer and waiting for this PR, you can add:

use HTTPoison.Base

@dialyzer {:nowarn_function, request!: 1}

to your modules that use HTTPoison.Base

[edgurgel]

2.2.1 is out! Thanks, team