Avoid Nullish coalescing operator to support old Node.js

[ai]

We are adding color.js to Stylelint for cool color-no-out-gamut-range rule.

But ?? operator from color.js sources breaks Node.js 12 and 14 support:

    /home/runner/work/stylelint/stylelint/node_modules/colorjs.io/dist/color.cjs:328
    		let coords = options.coords ?? this.base.coords;
    		                             ^

    SyntaxError: Unexpected token '?'

[LeaVerou]

Hm, I suppose we could add Babel for the generated bundles and use a NodeJS 12 target.