Add missing include (only MONOLITH builds were possible without it).

Submitted by: Andrew W. Gray

apps/spkac.c

@@ -63,6 +63,7 @@
 #include <time.h>
 #include "apps.h"
 #include <openssl/bio.h>
+#include <openssl/conf.h>
 #include <openssl/err.h>
 #include <openssl/evp.h>
 #include <openssl/lhash.h>