fix: deprecated function replaced

Author: danil-pavlov

Collections/Sum/src/Task.kt

@@ -1,3 +1,3 @@
 // Return the sum of prices for all the products ordered by a given customer
 fun moneySpentBy(customer: Customer): Double =
-        customer.orders.flatMap { it.products }.sumByDouble { it.price }
+        customer.orders.flatMap { it.products }.sumOf { it.price }

Collections/Sum/task-info.yaml

@@ -4,7 +4,7 @@ files:
   visible: true
   placeholders:
   - offset: 132
-    length: 64
+    length: 58
     placeholder_text: TODO()
 - name: src/Shop.kt
   visible: true

Collections/Sum/task.md

@@ -5,9 +5,8 @@ the sum of the prices for all the products ordered by a given customer.
 Note that each product should be counted as many times as it was ordered.
 
 Use
-[`sum`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sum.html) or
-[`sumOf`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sum-of.html).
-If you want to sum up double values, use `sumOfDouble`.
+[`sum`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sum.html) or 
+[`sumOf`](https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/sum-of.html), if you want to sum up double values.
 
 ```kotlin
 listOf(1, 5, 3).sum() == 9