xso: Use core instead of std wherever possible

xso/src/minidom_compat.rs

@@ -5,8 +5,8 @@
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
+use core::marker::PhantomData;
 use std::borrow::Cow;
-use std::marker::PhantomData;
 use std::vec::IntoIter;
 
 use minidom::{Element, Node};