journal-gatewayd: actually recognize -D as a synonym for --directory (#5180)

src/journal-remote/journal-gatewayd.c

@@ -912,7 +912,7 @@ static int parse_argv(int argc, char *argv[]) {
         assert(argc >= 0);
         assert(argv);
 
-        while ((c = getopt_long(argc, argv, "h", options, NULL)) >= 0)
+        while ((c = getopt_long(argc, argv, "hD:", options, NULL)) >= 0)
 
                 switch(c) {