bug#37729: "!${PATH}/date" path prefix in DEMO change directory is failing

[Kevin J. McCarthy]

I use:  Editor:      GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 
3.24.4)

        Hyperbole:   7.0.7
        Sys Type:    x86_64-pc-linux-gnu
        OS Type:     gnu/linux
        Window Sys:  x
        News Reader: Gnus v5.13

Trying to run the path prefix example in the DEMO file under

* Implicit Buttons
** Implicit Path Links
*** Path Prefixes

"!${PATH}/date" opens a shell window but tries to cd to the DEMO file 
instead of the directory it is in:

% cd /home/kjm/confs/home/.emacs.d/lib/hyperbole/DEMO; /bin/date
cd: not a directory: /home/kjm/confs/home/.emacs.d/lib/hyperbole/DEMO
Sun 13 Oct 2019 03:02:16 PM CST

I use a symlinks to my config files, that's why you see the directory 
path under ~/confs/home/.emacs.d instead of ~/.emacs.d.  But I don't 
think that would be causing an issue here.

It doesn't interfere with the date command running, but I wonder if this 
would affect other possible examples.

Thank you,

-Kevin