Fix rustc warning: remove extern crate std_unicode
diff --git a/src/lib.rs b/src/lib.rs
index 6dd06d5..af1e21c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -24,7 +24,6 @@
 extern crate log;
 #[cfg(unix)]
 extern crate nix;
-extern crate std_unicode;
 extern crate unicode_segmentation;
 extern crate unicode_width;
 #[cfg(windows)]