write version to stdout like the man page says

1 files changed, 1 insertions, 1 deletions

diff --git a/slock.c b/slock.c
index 5ae738c..b2f14e3 100644
--- a/slock.c
+++ b/slock.c
@@ -317,7 +317,7 @@ main(int argc, char **argv) {
 
 	ARGBEGIN {
 	case 'v':
-		fprintf(stderr, "slock-"VERSION"\n");
+		puts("slock-"VERSION);
 		return 0;
 	default:
 		usage();