Update hellogl.py

Fixed type for python 3.x
Traceback (most recent call last):
  File "gltemp.py", line 129, in resizeGL
    GL.glViewport((width - side) / 2, (height - side) / 2, side, side)
ctypes.ArgumentError: argument 1: <class 'TypeError'>: wrong type
Merge pull request #13 from Lazik/patch-2

Update hellogl.py