Make this work on old git (1.7).

(cherry picked from commit b479182cd27faa9849b88245663bb5e56f3bc581)
Signed-off-by: Bruce A. Mah <bmah@es.net>
diff --git a/make_release b/make_release
index 3213e20..b874597 100755
--- a/make_release
+++ b/make_release
@@ -21,7 +21,7 @@
 
 do_tag ()
 {
-    git tag --sign -m "tagging $tag" $tag
+    git tag -s -m "tagging $tag" $tag
 }
 
 do_tar ()