`epath.Path.touch()` does not update mtime

The documentation of [`pathlib.Path.touch`](https://docs.python.org/3/library/pathlib.html#pathlib.Path.touch):

> Create a file at this given path. If mode is given, it is combined with the process’ umask value to determine the file mode and access flags. If the file already exists, the function succeeds if exist_ok is true (and its modification time is updated to the current time), otherwise [FileExistsError](https://docs.python.org/3/library/exceptions.html#FileExistsError) is raised.

According to this documentation, `touch()` should update the file's modification time to the current time. However, `epath.Path.touch()` does not match this behaviour.