Update shutil.rst

Filenames containing two dots ".." do not necessarily indicate relative path components. Only "../" identify a relative path component.

Author: sepastian

Doc/library/shutil.rst

@@ -703,7 +703,7 @@ provided.  They rely on the :mod:`zipfile` and :mod:`tarfile` modules.
       Never extract archives from untrusted sources without prior inspection.
       It is possible that files are created outside of the path specified in
       the *extract_dir* argument, e.g. members that have absolute filenames
-      starting with "/" or filenames with two dots "..".
+      starting with "/" or filenames with relative path components "../".
 
    .. versionchanged:: 3.7
       Accepts a :term:`path-like object` for *filename* and *extract_dir*.