Docs: Fix mistake in Color#getRGB signature

[donmccurdy]

The getRGB method returns colors in the working color space by default (Linear-sRGB), not sRGB.

three.js/src/math/Color.js

Lines 412 to 422 in 14ba689

	getRGB( target, colorSpace = ColorManagement.workingColorSpace ) {
	ColorManagement.fromWorkingColorSpace( _color.copy( this ), colorSpace );
	target.r = _color.r;
	target.g = _color.g;
	target.b = _color.b;
	return target;
	}