Destroy contents when removing view

examples/spreads.html

@@ -33,7 +33,7 @@
 
     rendition.display(currentSectionIndex);
 
-    book.ready.then(() => {
+    book.ready.then(function() {
 
       var next = document.getElementById("next");
 

src/contents.js

@@ -450,7 +450,6 @@ class Contents {
 		clearTimeout(this.expanding);
 
 		requestAnimationFrame(this.resizeCheck.bind(this));
-
 		this.expanding = setTimeout(this.resizeListeners.bind(this), 350);
 	}
 

src/managers/views/iframe.js

@@ -780,6 +780,7 @@ class IframeView {
 			this.displayed = false;
 
 			this.removeListeners();
+			this.contents.destroy();
 
 			this.stopExpanding = true;
 			this.element.removeChild(this.iframe);