Fix missing prototype declarations

Signed-off-by: Peter Colberg <peter@colberg.org>
diff --git a/ui-refs.h b/ui-refs.h
index b35c04a..1d4a54a 100644
--- a/ui-refs.h
+++ b/ui-refs.h
@@ -3,6 +3,6 @@
 
 extern void cgit_print_branches(int maxcount);
 extern void cgit_print_tags(int maxcount);
-extern void cgit_print_refs();
+extern void cgit_print_refs(void);
 
 #endif /* UI_REFS_H */