Add Theo Spears to contributors.txt

CONTRIBUTORS.txt

@@ -129,3 +129,4 @@ Jun Sakai, 2013/01/16
 Vlad Frolov, 2013/01/23
 Milen Pavlov, 2013/03/08
 Pär Wieslander, 2013/03/20
+Theo Spears, 2013/03/28