message: Use Cow<str> when normalizing parent url path
diff: @@ -11,6 +11,7 @@ use git2::{self, ErrorClass, ObjectType, Oid};
  use log::{debug, info};
  use serde::ser;
  use serde::Serialize;
  +use std::borrow::Cow;
  use std::env;
  use std::fmt;
  use std::path::{Path, PathBuf};
  @@ -373,9 +374,9 @@ impl<'a> GitCheckout<'a> {
  // See the `git submodule add` command on the documentation:
  // https://git-scm.com/docs/git-submodule
  let url = if child_url_str.starts_with("./") || child_url_str.starts_with("../") {
  - let mut new_path = parent_remote_url.path().to_string();
  + let mut new_path = Cow::from(parent_remote_url.path());
  if !new_path.ends_with('/') {
  - new_path.push('/');
  + new_path.to_mut().push('/');
  }
  let mut new_parent_remote_url = parent_remote_url.clone();
  