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/security/transform/digest-filter.t.cpp b/tests/unit/security/transform/digest-filter.t.cpp
index 67ccc4c..984611d 100644
--- a/tests/unit/security/transform/digest-filter.t.cpp
+++ b/tests/unit/security/transform/digest-filter.t.cpp
@@ -22,7 +22,7 @@
 #include "ndn-cxx/security/transform/digest-filter.hpp"
 
 #include "ndn-cxx/encoding/buffer-stream.hpp"
-#include "ndn-cxx/security/detail/openssl.hpp"
+#include "ndn-cxx/security/impl/openssl.hpp"
 #include "ndn-cxx/security/transform/buffer-source.hpp"
 #include "ndn-cxx/security/transform/step-source.hpp"
 #include "ndn-cxx/security/transform/stream-sink.hpp"