Filter out img sizes

https://github.com/FreshRSS/FreshRSS/issues/1077
https://github.com/FreshRSS/FreshRSS/issues/1081

lib/lib_rss.php

@@ -209,7 +209,7 @@ function customSimplePie() {
 	$simplePie->strip_attributes(array_merge($simplePie->strip_attributes, array(
 		'autoplay', 'onload', 'onunload', 'onclick', 'ondblclick', 'onmousedown', 'onmouseup',
 		'onmouseover', 'onmousemove', 'onmouseout', 'onfocus', 'onblur',
-		'onkeypress', 'onkeydown', 'onkeyup', 'onselect', 'onchange', 'seamless', 'srcset')));
+		'onkeypress', 'onkeydown', 'onkeyup', 'onselect', 'onchange', 'seamless', 'sizes', 'srcset')));
 	$simplePie->add_attributes(array(
 		'img' => array('lazyload' => '', 'postpone' => ''),	//http://www.w3.org/TR/resource-priorities/
 		'audio' => array('lazyload' => '', 'postpone' => '', 'preload' => 'none'),