Changed extension in parsing test data (jet -> kt)

compiler/testData/psi/examples/UpdateOperation.kt

@@ -0,0 +1,14 @@
+class Pair(x : Int, y : Int) {
+  class object {
+    fun copy(from : Pair, x : Int = from.x, y : Int = from.y) = Pair(x, y)
+  }
+}
+
+// One can say:
+val p = Point(1, 2)
+val p1 = Point.Copy(p, x = 2)
+val p2 = Point.Copy(p1, y = -1)
+val p3 = Point.Copy(p)
+
+// Such copy(...) methods can be automatically generated by the compiler
+// whenever there is a primary constructor