Fix PiWS281X.set_brightness (fix #715)
Fix PiWS281X.set_brightness (fix #715)

* See https://github.com/jgarff/rpi_ws281x/blob/master/python/neopixel.py#L127

rec/BiblioPixel,rec/BiblioPixel,rec/BiblioPixel,rec/BiblioPixel,ManiacalLabs/BiblioPixel,ManiacalLabs/BiblioPixel,ManiacalLabs/BiblioPixel,ManiacalLabs/BiblioPixel