Have delete borrow its element

As discussed here
exercism#114 (diff)

Author: whit0694

exercises/custom-set/example.rs

@@ -25,8 +25,8 @@ impl<T: Ord + Clone> CustomSet<T> {
         }
     }
 
-    pub fn delete(&mut self, element: T) {
-        self.collection.retain(|x| x != &element)
+    pub fn delete(&mut self, element: &T) {
+        self.collection.retain(|x| x != element)
     }
 
     pub fn contains(&self, other: &T) -> bool {

exercises/custom-set/tests/custom-set.rs

@@ -82,14 +82,14 @@ fn add_existing_element() {
 #[test]
 fn delete_an_existing_element() {
     let mut set = CustomSet::new(vec![3, 2, 1]);
-    set.delete(2);
+    set.delete(&2);
     assert_eq!(set, CustomSet::new(vec![1, 3]));
 }
 
 #[test]
 fn delete_an_nonexistent_element() {
     let mut set = CustomSet::new(vec![3, 2, 1]);
-    set.delete(4);
+    set.delete(&4);
     assert_eq!(set, CustomSet::new(vec![1, 2, 3]));
 }