Corrige error en jquery 3 (markdalgleish#147)

Author: ceronetowner

jquery.stellar.js

@@ -2,7 +2,7 @@
  * Stellar.js v0.6.2
  * http://markdalgleish.com/projects/stellar.js
  *
- * Copyright 2014, Mark Dalgleish
+ * Copyright 2017, Mark Dalgleish
  * This content is released under the MIT license
  * http://markdalgleish.mit-license.org
  */
@@ -234,7 +234,7 @@
 
 			// Fix for WebKit background rendering bug
 			if (options && options.firstLoad && /WebKit/.test(navigator.userAgent)) {
-				$(window).load(function() {
+				$(window).on('load', function() {
 					var oldLeft = self._getScrollLeft(),
 						oldTop = self._getScrollTop();
 
@@ -250,7 +250,7 @@
 			this._setScrollTop(oldTop);
 		},
 		_detectViewport: function() {
-			var viewportOffsets = this.$viewportElement.offset(),
+                        var viewportOffsets = this.$viewportElement[0] !== window ? this.$viewportElement.offset() : {top: 0, left: 0},
 				hasOffsets = viewportOffsets !== null && viewportOffsets !== undefined;
 
 			this.viewportWidth = this.$viewportElement.width();
@@ -657,4 +657,4 @@
 
 	// Expose the plugin class so it can be modified
 	window.Stellar = Plugin;
-}(jQuery, this, document));
+}(jQuery, this, document));