Can't use multiple custom classes

[Tadaz]

Thanks for the great package guys.

One minor issue I found so far, it fails while trying to pass a string or an array containing multiple custom classes.

Example:

new Notify({
        customClass: 'mycustomclass-1 mycustomclass-2'
})

Exception's location:

Notify.prototype.setWrapper = function () {
        var wrapper = document.createElement('div');
        this.wrapper = wrapper;
        this.wrapper.style.setProperty('--gap', this.gap + "px");
        this.wrapper.style.transitionDuration = this.speed + "ms";
        // set classes
        this.wrapper.classList.add('notify');
        this.wrapper.classList.add("notify--type-" + this.type);
        this.wrapper.classList.add("notify--" + this.status);
        if (this.customClass)
            this.wrapper.classList.add(this.customClass); //FAILS HERE
    };

Works fine if you pass only one class though.