fix quote import

This always has been an alias for backwards compatibility: https://github.com/python/cpython/blob/1a104e51129b6ec5a433241f3acf329cf692be94/Lib/pipes.py#L64-L66

ocrodjvu/ipc.py

@@ -19,8 +19,8 @@
 import errno
 import logging
 import os
-import pipes
 import re
+import shlex
 import signal
 import subprocess