py-sh: updated to 1.13.1

1.13.1:
* regression fix if `_fg=False`

1.13.0:
* minor Travis CI fixes
* bugfix for boolean long options not respecting `_long_prefix`
* fix deprecation warning on Python 3.6 regexes
* `_pass_fds` and `_close_fds` special kwargs for controlling file descriptor inheritance in child.
* more efficiently closing inherited fds
* bugfix where passing invalid dictionary to `_env` will cause a mysterious child 255 exit code.
* bugfix where `_in` using 0 or `sys.stdin` wasn't behaving like a TTY, if it was in fact a TTY.
* bugfix where `help(sh)` raised an exception
* bugfix fixing broken interactive ssh tutorial from docs
* change to automatic tty merging into a single pty if `_tty_in=True` and `_tty_out=True`
* introducing `_unify_ttys`, default False, which allows explicit tty merging into single pty
* contrib command for `ssh` connections requiring passwords
* performance fix for polling output too fast when using `_iter`
* execution contexts can now be used in python shell
* bugfix `ErrorReturnCode` instances can now be pickled
* bugfix passing empty string or `None` for `_in` hanged
* bugfix where passing a filename or file-like object to `_out` wasn't using os.dup2
* regression make `_fg` work with `_cwd` again
* an invalid `_cwd` now raises a `ForkException` not an `OSError`.
* AIX support
* added a `timeout=None` param to `RunningCommand.wait()`


(adam)