c/util: Making util/crypto.h a public header

Change-Id: Ie63d3b5b206ae7e027e11077b6c0a039ed75eb92
diff --git a/src/c/util/crypto.c b/src/c/util/crypto.c
index ec13f68..e8dfbfd 100644
--- a/src/c/util/crypto.c
+++ b/src/c/util/crypto.c
@@ -4,7 +4,7 @@
  * See COPYING for copyright and distribution information.
  */
 
-#include "crypto.h"
+#include "ndn-cpp/c/util/crypto.h"
 
 void ndn_digestSha256(const uint8_t *data, size_t dataLength, uint8_t *digest)
 {