impl: rename 'detail' to 'impl'

'impl' directory contains implementation-detail headers that are NOT
installed. 'detail' directory will be used for implementation-detail
headers that ARE installed.

refs #4782

Change-Id: I13428e032c93207753a6b856c693511c4fc3bbb8
diff --git a/tests/unit/util/random.t.cpp b/tests/unit/util/random.t.cpp
index ee55f9e..9cf7325 100644
--- a/tests/unit/util/random.t.cpp
+++ b/tests/unit/util/random.t.cpp
@@ -20,7 +20,7 @@
  */
 
 #include "ndn-cxx/util/random.hpp"
-#include "ndn-cxx/security/detail/openssl.hpp"
+#include "ndn-cxx/security/impl/openssl.hpp"
 
 #include "tests/boost-test.hpp"