error: unused import: `std::ascii::AsciiExt`
  --> /wrkdirs/usr/ports/www/firefox/work/firefox-57.0.4/servo/components/style/gecko_string_cache/mod.rs:16:5
   |
16 | use std::ascii::AsciiExt;
   |     ^^^^^^^^^^^^^^^^^^^^
   |
note: lint level defined here
  --> /wrkdirs/usr/ports/www/firefox/work/firefox-57.0.4/servo/components/style/lib.rs:26:9
   |
26 | #![deny(warnings)]
   |         ^^^^^^^^
   = note: #[deny(unused_imports)] implied by #[deny(warnings)]