bad_style doesn't fire for associated types

[est31]

Associated types are types and thus should be capitalized. I think most code also does this. Recently I accidentally didn't capitalize it and was surprised that it doesn't lint for it:

pub trait Foo {
    type hello;
}

I'd expect it to say something.

This issue has been assigned to @Fibration via this comment.

[csmoe]

bad_style checking happens inside src/librustc_lint/nonstandard_style.rs, add check_trait_item for NonCamelCaseTypes, then inspect the kind of AssocitemKind inside this checking.

[Fibration]

I'd like to put my hand up for this if that's alright? It looks like a good one to get started on.

@rustbot claim