fix typo in push documentation

Author: 20jasper

library/alloc/src/vec/mod.rs

@@ -1922,7 +1922,7 @@ impl<T, A: Allocator> Vec<T, A> {
     /// # Time complexity
     ///
     /// Takes amortized *O*(1) time. If the vector's length would exceed its capacity after
-    /// the push,*O*(*capacity*) space is allocated, doubling the capacity and
+    /// the push, *O*(*capacity*) space is allocated, doubling the capacity and
     /// taking *O*(*capacity*) time. This expensive operation is offset by the
     /// *capacity* *O*(1) insertions it allows.
     #[cfg(not(no_global_oom_handling))]