Update CONTRIBUTORS.txt

Added myself, and fixed the dates of the other 2014 additions.

CONTRIBUTORS.txt

@@ -152,5 +152,6 @@ Michael Robellard, 2013/11/07
 Vsevolod Kulaga, 2013/11/16
 Ionel Cristian Mărieș, 2013/12/09
 Константин Подшумок, 2013/12/16
-Antoine Legrand, 2014/09/01
-Pepijn de Vos, 2014/15/01
+Antoine Legrand, 2014/01/09
+Pepijn de Vos, 2014/01/15
+Dan McGee, 2014/01/27