Gray::toRgb rounding error

[AntonioDiPassio-AppSys]

line 34:
return new Rgb((int) ($this->gray * 2.55), (int) ($this->gray * 2.55), (int) ($this->gray * 2.55));

If $this->gray is 100, it will return Rgb(254,254,254)

because PHP being weird and: (int) (100 * 2.55) = 254

Can be fixed by changing it to:
return new Rgb((int) ($this->gray * 255 / 100), (int) ($this->gray * 255 / 100), (int) ($this->gray * 255 / 100));

[DASPRiD]

Feel free to supply a PR with a matching test :)