Escape keys in case one is a reserved word

[jblandry]

If I have a JSON like this:

{
	"colors": {
		"yellow": "#ffff00"
	}
}

it outputs

$colors: (yellow: #ffff00);

But I can't access it because yellow isn't considered a string but a color.

So I changed the generation to

$colors: ('yellow': #ffff00);

so I can access it.

(Tested with DartSass 1.6.2)