fixing tmx color problem in py2.X

Hello,

I noticed in tiles.py, line 1789 that we call pyglet.image.SolidColorImagePattern(color) with color being a list.
But in pyglet, it seems that SolidColorImagePattern requires a tuple.

If we are under Python 2, we come in the function
```
def color_as_bytes(color):
    if sys.version.startswith('2'):
        return '%c%c%c%c' % color
    else:
        if len(color) != 4:
            raise TypeError("color is expected to have 4 components")
        return bytes(color)
```
and ```'%c%c%c%c' % [128]*4``` would produce an exception.

I guess the easy fix would be in tiles.py to have on line 1788
```color = tuple(self.color[:3] + [128])```