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/pib/key.t.cpp b/tests/unit/security/pib/key.t.cpp
index 86f7dfa..8dfe9c8 100644
--- a/tests/unit/security/pib/key.t.cpp
+++ b/tests/unit/security/pib/key.t.cpp
@@ -22,7 +22,7 @@
 #include "ndn-cxx/security/pib/key.hpp"
 #include "ndn-cxx/security/pib/pib.hpp"
 #include "ndn-cxx/security/pib/pib-memory.hpp"
-#include "ndn-cxx/security/pib/detail/key-impl.hpp"
+#include "ndn-cxx/security/pib/impl/key-impl.hpp"
 
 #include "tests/boost-test.hpp"
 #include "tests/unit/security/pib/pib-data-fixture.hpp"