Use new kotlin.io.path API in tests

compiler/incremental-compilation-impl/test/org/jetbrains/kotlin/incremental/BuildDiffsStorageTest.kt

@@ -22,6 +22,7 @@ import org.junit.Assert
 import org.junit.Before
 import org.junit.Test
 import java.io.File
+import java.nio.file.Files
 import java.util.*
 
 class BuildDiffsStorageTest {
@@ -30,7 +31,7 @@ class BuildDiffsStorageTest {
 
     @Before
     fun setUp() {
-        storageFile = File.createTempFile("BuildDiffsStorageTest", "storage")
+        storageFile = Files.createTempFile("BuildDiffsStorageTest", "storage").toFile()
     }
 
     @After