Feature request: support for #rgba shortcut

[antonk52]

Hi and thank you for your work. The plugin already supports 6 character hex colours, 3 character hex shortcut, and 8 character hex color with alpha component. It would be great to also add support for 4 character hex color with alpha channel.

Example

body {
  color: #ff0000;
  color: #f00;
  color: #ff000000;
  color: #f000; /* not highlighted */
}

Related MDN documentation about hex color

Thanks!