rustdoc: Include impl [u8] in the docs

Author: ollie27

src/librustdoc/clean/inline.rs

@@ -269,6 +269,7 @@ pub fn build_impls(cx: &DocContext, did: DefId) -> Vec<clean::Item> {
         lang_items.char_impl(),
         lang_items.str_impl(),
         lang_items.slice_impl(),
+        lang_items.slice_u8_impl(),
         lang_items.const_ptr_impl(),
         lang_items.mut_ptr_impl(),
     ];