remove iframe not work correctly

[gimox]

Sometime loading multiple book can generate error because iframe is not correctly removed.

EPUBJS.Renderer.prototype.remove = function() {
    if(this.render.window) {
        this.render.unload();
        this.render.window.removeEventListener("resize", this.resized);
        this.removeEventListeners();
        this.removeSelectionListeners();
    }

    // clean container content 
    this.container.innerHtml = "";
//  this.container.removeChild(this.element);
};

the issue is on cleaning container instead of remove it.

My proposal is for re-add/uncomment removeChild that is always safe.

EPUBJS.Renderer.prototype.remove = function() {
    if(this.render.window) {
        this.render.unload();
        this.render.window.removeEventListener("resize", this.resized);
        this.removeEventListeners();
        this.removeSelectionListeners();
    }

    // clean container content 
    //this.container.innerHtml = "";
    this.container.removeChild(this.element);
};

[fchasen]

That sounds like a good solution, not sure why the innerHtml ended up there.

A PR with that change would be very appreciated.