fill() incorrectly used instead of stroke() on point() reference page example

[per1234]

https://www.arduino.cc/en/Reference/TFTPoint

Change:

  // set the stroke color to white
  screen.fill(255,255,255);

to:

  // set the stroke color to white
  screen.stroke(255,255,255);

Originally reported at http://forum.arduino.cc/index.php?topic=494624