middleware example: print out both headers and options

[JLarky]

I was looking at https://hexdocs.pm/tesla/Tesla.Middleware.html docs that were for 1.4.4 and noticed that the middleware example doesn't work. I wanted to fix it, but noticed that here on GitHub this code is already updated, but it still has some issues. I can imagine that originally it was indeed intended to use middleware options as options for IO.inspect/2 but I am more inclined to believe that options were passed to IO.inspect just so the compiler wouldn't complain about the unused variable :) so I think it would be better to either print the options out or just remove them completely and replace them with _options.

p.s. the first time I'm contributing to this project. So I will use this opportunity to say that your library is very cool and I'm happy using it :)

[teamon]

Good catch!

For the sake of simplicity I think we should go with:

def call(env, next, _opts) do
  IO.inspect(env.headers)

[yordis]

🚀