Added myself to the contributors list

CONTRIBUTORS.txt

@@ -234,3 +234,4 @@ Arcadiy Ivanov, 2017/01/08
 Ryan Hiebert, 2017/01/20
 Jianjian Yu, 2017/04/09
 Brian May, 2017/04/10
+Dmytro Petruk, 2017/04/12