security: Add doxygen comments

Change-Id: Ieafe4d13513e626d84ef9e621694f69844785018
diff --git a/src/security/sec-public-info-memory.cpp b/src/security/sec-public-info-memory.cpp
index e9f93f2..1e41df1 100644
--- a/src/security/sec-public-info-memory.cpp
+++ b/src/security/sec-public-info-memory.cpp
@@ -219,6 +219,4 @@
   throw runtime_error("SecPublicInfoMemory::deleteIdentityInfo not implemented");
 }
 
-
-
-}
+} // namespace ndn