grdc: fprintf(stderr -> warnx

[Scott Cheloha]

Just use warnx.

--
Scott Cheloha

Index: games/grdc/grdc.c
===================================================================
RCS file: /cvs/src/games/grdc/grdc.c,v
retrieving revision 1.26
diff -u -p -r1.26 grdc.c
--- games/grdc/grdc.c   7 Mar 2016 12:07:56 -0000       1.26
+++ games/grdc/grdc.c   8 Jul 2017 15:22:39 -0000
@@ -90,7 +90,7 @@ main(int argc, char *argv[])
        if (argc == 1) {
                n = strtonum(*argv, 1, INT_MAX, &errstr);
                if (errstr) {
-                       fprintf(stderr, "number of seconds is %s\n", errstr);
+                       warnx("number of seconds is %s", errstr);
                        usage();
                }
        }