Fix Kotlin template

Author: ileasile

kotlin/sprint2/B/Solution.kt

@@ -1,5 +1,8 @@
 // <template>
-class Node<V>(var value: V, var next: Node<V>?) {}
+class Node<V>(
+    var value: V,
+    var next: Node<V>? = null,
+) {}
 // <template>
 
 fun solution(head: Node<String>?) {
@@ -20,4 +23,4 @@ fun test() {
     node2
     node3
     */
-}
+}