Update CONTRIBUTORS.txt

CONTRIBUTORS.txt

@@ -132,3 +132,4 @@ Pär Wieslander, 2013/03/20
 Theo Spears, 2013/03/28
 Romuald Brunet, 2013/03/29
 Aaron Harnly, 2013/04/04
+Peter Brook, 2013/05/09