[Gradle, JS] Use API form Gradle 5.0

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/ir/KotlinJsIrSubTarget.kt

@@ -106,7 +106,7 @@ abstract class KotlinJsIrSubTarget(
             ).single().linkTask
 
             testJs.inputFileProperty.set(
-                testExecutableTask.map { it.outputFileProperty.get() }
+                testExecutableTask.flatMap { it.outputFileProperty }
             )
 
             testJs.dependsOn(nodeJs.npmInstallTask, nodeJs.nodeJsSetupTask)

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/targets/js/ir/KotlinNodeJsIr.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -35,7 +35,7 @@ open class KotlinNodeJsIr @Inject constructor(target: KotlinJsIrTarget) :
             .all { developmentExecutable ->
                 val runTaskHolder = NodeJsExec.create(compilation, disambiguateCamelCased(RUN_TASK_NAME)) {
                     group = taskGroupName
-                    inputFileProperty.set(developmentExecutable.linkTask.map { it.outputFileProperty.get() })
+                    inputFileProperty.set(developmentExecutable.linkTask.flatMap { it.outputFileProperty })
                 }
 
                 target.runTask.dependsOn(runTaskHolder)