object empty key string should be supported

[iwind]

To set an object property value, we are able to call Set() method in object.go:

func (o *Object) Set(key string, val interface{}) error {
	if len(key) == 0 {
		return errors.New("v8go: You must provide a valid property key")
	}
        ...
}

But, it does not accept an empty string key, which should be valid in javascript:

let obj = {}
obj[""] = "Empty Key Value" // this will be valid in all of Javascript engines

So, empty string key should be available in v8go.