rename identity challenge dir to challenge

Change-Id: Ieb89704404dae2086bd83987624670432bb69663
diff --git a/src/detail/ca-profile.cpp b/src/detail/ca-profile.cpp
index bd826e9..5216ae0 100644
--- a/src/detail/ca-profile.cpp
+++ b/src/detail/ca-profile.cpp
@@ -19,7 +19,7 @@
  */
 
 #include "detail/ca-profile.hpp"
-#include "identity-challenge/challenge-module.hpp"
+#include "challenge/challenge-module.hpp"
 #include <ndn-cxx/util/io.hpp>
 #include <boost/filesystem.hpp>