fix: revert primitive_types4 (#296)

Author: jrvidal

exercises/primitive_types/primitive_types4.rs

@@ -8,4 +8,7 @@
 fn slice_out_of_array() {
     let a = [1, 2, 3, 4, 5];
 
+    let nice_slice = ???
+
+    assert_eq!([2, 3, 4], nice_slice)
 }