quickcheck_macros: Update for rust-lang/rust#37824

[andersk]

“Clean up ast::Attribute, ast::CrateConfig, and string interning”

Resolves these errors:

error[E0425]: unresolved name `token::intern`
  --> src/lib.rs:27:35
   |
27 |     reg.register_syntax_extension(token::intern("quickcheck"),
   |                                   ^^^^^^^^^^^^^ unresolved name

error[E0425]: unresolved name `token::str_to_ident`
  --> src/lib.rs:86:23
   |
86 |     let check_ident = token::str_to_ident("quickcheck");
   |                       ^^^^^^^^^^^^^^^^^^^ unresolved name

error[E0425]: unresolved name `token::intern_and_get_ident`
   --> src/lib.rs:107:34
    |
107 |         span, cx.meta_word(span, token::intern_and_get_ident("test"))));
    |                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^ unresolved name

error: aborting due to 3 previous errors

[BurntSushi]

Awesome, thank you!

[emberian]

@BurntSushi did this actually get deployed with 0.4? I'm still getting this error.

[BurntSushi]

@cmr Whoops, I forgot to do a release. Done now! Thanks for the ping!