Update maintainerlist from github info (DOMjudge#43)

Author: vmcj

website/about.shtml

@@ -67,8 +67,8 @@ administrator manual</a>.</p>
 <h2>Authors and contact</h2>
 
 <p>The main developers are Jaap Eldering, Nicky Gerritsen, Keith
-Johnson, Thijs Kinkhorst, and Tobias Werth, with contributions from
-many other people.
+Johnson, Thijs Kinkhorst, Mart Pluijmaekers, Michael Vasseur and Tobias Werth,
+with contributions from many other people.
 Anyone interested is welcome to <a href="development">contribute to DOMjudge</a>.</p>
 
 <p>The project is licensed under the GNU General Public Licence. This gives