Resolve mem_replace_with_default clippy lint

    warning: replacing a value of type `T` with `T::default()` is better expressed using `std::mem::take`
      --> src/rcvec.rs:56:13
       |
    56 |             mem::replace(owned, Vec::new())
       |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: consider using: `std::mem::take(owned)`
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#mem_replace_with_default
       = note: `-W clippy::mem-replace-with-default` implied by `-W clippy::all`

Author: dtolnay

src/rcvec.rs

@@ -53,7 +53,7 @@ impl<T> RcVec<T> {
         T: Clone,
     {
         let vec = if let Some(owned) = Rc::get_mut(&mut self.inner) {
-            mem::replace(owned, Vec::new())
+            mem::take(owned)
         } else {
             Vec::clone(&self.inner)
         };