remove protobuf dependency

Change-Id: I10bf90ba940bbde27d91df58056f4f558843f697
diff --git a/src/endorse-certificate.hpp b/src/endorse-certificate.hpp
index d215a22..51b3b50 100644
--- a/src/endorse-certificate.hpp
+++ b/src/endorse-certificate.hpp
@@ -6,6 +6,7 @@
  * BSD license, See the LICENSE file for more information
  *
  * Author: Yingdi Yu <yingdi@cs.ucla.edu>
+ *         Qiuhan Ding <qiuhanding@cs.ucla.edu>
  */
 
 #ifndef CHRONOCHAT_ENDORSE_CERTIFICATE_HPP