Use inherent usize::div_ceil

Author: cuviper

src/map.rs

@@ -1825,10 +1825,11 @@ where
         // Otherwise reserve half the hint (rounded up), so the map
         // will only resize twice in the worst case.
         let iter = iterable.into_iter();
+        let (lower_len, _) = iter.size_hint();
         let reserve = if self.is_empty() {
-            iter.size_hint().0
+            lower_len
         } else {
-            (iter.size_hint().0 + 1) / 2
+            lower_len.div_ceil(2)
         };
         self.reserve(reserve);
         iter.for_each(move |(k, v)| {