Skip ssh.ibt doctest since some runners appear to support it now

Author: peace-maker

pwnlib/tubes/ssh.py

@@ -2181,7 +2181,7 @@ def ibt(self):
         Example:
 
             >>> s = ssh("travis", "example.pwnme")
-            >>> s.ibt
+            >>> s.ibt # doctest: +SKIP 
             False
         """
         if self._ibt is None: