fix warning by using iter() instead of into_iter()

Change into_iter() to iter() in impl_zip_iter macro
to avoid the compliation warning related to
s://github.com/rust-lang/rust/issues/66145.

src/ziptuple.rs

@@ -39,8 +39,9 @@ pub struct Zip<T> {
 /// assert_eq!(results, [0 + 3, 10 + 7, 29, 36]);
 /// ```
 pub fn multizip<T, U>(t: U) -> Zip<T>
-    where Zip<T>: From<U>,
-          Zip<T>: Iterator,
+where
+    Zip<T>: From<U>,
+    Zip<T>: Iterator,
 {
     Zip::from(t)
 }
@@ -108,7 +109,7 @@ macro_rules! impl_zip_iter {
             #[inline]
             fn next_back(&mut self) -> Option<Self::Item> {
                 let ($(ref mut $B,)*) = self.t;
-                let size = *[$( $B.len(), )*].into_iter().min().unwrap();
+                let size = *[$( $B.len(), )*].iter().min().unwrap();
 
                 $(
                     if $B.len() != size {