Escape HashMap with backticks in needs_drop docs

src/libcore/mem/mod.rs

@@ -374,7 +374,7 @@ pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
 /// will do a single needs_drop check for all the values.
 ///
 /// Types like Vec therefore just `drop_in_place(&mut self[..])` without using
-/// needs_drop explicitly. Types like HashMap, on the other hand, have to drop
+/// needs_drop explicitly. Types like `HashMap`, on the other hand, have to drop
 /// values one at a time and should use this API.
 ///
 ///