add Matthijs van Henten to the about box

plugins/c9.ide.help/help.xml

@@ -23,7 +23,7 @@
                 <p textselect="true">
                     Bas de Wachter, Fabian Jakobs, Harutyun Amirjanyan,
                     Ivar Pruijn, Lennart Kats, Luca Cipriani,
-                    Mostafa Eweda, Nikolai Onken, Tim Robinson, Ruben Daniels
+                    Mostafa Eweda, Matthijs van Henten, Nikolai Onken, Tim Robinson, Ruben Daniels
                 </p>
             </div>
             <div class="c9Copyright">