Use File.getParentFile() in Sketch constructor

No need to call the File constructor ourselves, if
`File.getParentFile()` can just do that for us.

Author: matthijskooijman

arduino-core/src/processing/app/Sketch.java

@@ -46,7 +46,7 @@ public int compare(SketchFile x, SketchFile y) {
    *          Any file inside the sketch directory.
    */
   Sketch(File file) throws IOException {
-    folder = new File(file.getParent());
+    folder = file.getParentFile();
     files = listSketchFiles(true);
   }