Documentation fix on arguments to CookieAuthFileGroupReadable

We don't actually allow a group name, but the documentation implied
that we did.

doc/tor.1.txt

@@ -319,7 +319,7 @@ GENERAL OPTIONS
     If set, this option overrides the default location and file name
     for Tor's cookie file. (See CookieAuthentication above.)
 
-[[CookieAuthFileGroupReadable]] **CookieAuthFileGroupReadable** **0**|**1**|__Groupname__::
+[[CookieAuthFileGroupReadable]] **CookieAuthFileGroupReadable** **0**|**1**::
     If this option is set to 0, don't allow the filesystem group to read the
     cookie file. If the option is set to 1, make the cookie file readable by
     the default GID. [Making the file readable by other groups is not yet