fix typo in binary_heap docs

Author: Treeniks

alloc/src/collections/binary_heap/mod.rs

@@ -31,7 +31,7 @@
 //! // instead of a max-heap.
 //! impl Ord for State {
 //!     fn cmp(&self, other: &Self) -> Ordering {
-//!         // Notice that the we flip the ordering on costs.
+//!         // Notice that we flip the ordering on costs.
 //!         // In case of a tie we compare positions - this step is necessary
 //!         // to make implementations of `PartialEq` and `Ord` consistent.
 //!         other.cost.cmp(&self.cost)