Improve replace colors

[bilelmoussaoui]

For now, you should give the exact hex colors in order to replace them; Because we use the simply replace method. We should move to using Regex instead.
Should be done here https://github.com/bil-elmoussaoui/Hardcode-Tray/blob/master/modules/utils.py#L318

also if the user uses --replace-colors "#fff #000" and there's only #ffffff defined in the SVG file, it will break the things, so we should always use 6 hexadecimal instead of 3!