Add missing #include

According to POSIX.1-2001, dirname() is declared in libgen.h.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

credential-cache--daemon.c

@@ -1,6 +1,7 @@
 #include "cache.h"
 #include "credential.h"
 #include "unix-socket.h"
+#include <libgen.h>
 
 struct credential_cache_entry {
 	struct credential item;