rename identity challenge dir to challenge

Change-Id: Ieb89704404dae2086bd83987624670432bb69663
diff --git a/src/name-assignment/assignment-func.hpp b/src/name-assignment/assignment-func.hpp
index 29b516a..9e9b128 100644
--- a/src/name-assignment/assignment-func.hpp
+++ b/src/name-assignment/assignment-func.hpp
@@ -62,7 +62,7 @@
   createNameAssignmentFunc(const std::string& challengeType, const std::string& format = "");
 
 NDNCERT_PUBLIC_WITH_TESTS_ELSE_PROTECTED:
-    std::vector<std::string> m_nameFormat;
+  std::vector<std::string> m_nameFormat;
 
 private:
   typedef function<unique_ptr<NameAssignmentFunc>(const std::string&)> FactoryCreateFunc;