security: Add "explicit" markers for one-parameter constructors

Change-Id: I072c924ecdd212d63700804e8af3f4fac6da1919
Refs: #1681
diff --git a/src/security/certificate.hpp b/src/security/certificate.hpp
index 3fcea67..eff2bbc 100644
--- a/src/security/certificate.hpp
+++ b/src/security/certificate.hpp
@@ -59,6 +59,7 @@
    * Create a Certificate from the content in the data packet.
    * @param data The data packet with the content to decode.
    */
+  explicit
   Certificate(const Data& data);
 
   /**