Fix link normalization for live HTMLCollections

Newer versions of JSDOM implement getElementsByTagName correctly.
This means it returns a live node list. When calling
`Element.replaceChild` for links inside the loop over that
collection, elements disappear from the list, meaning we miss
every other item. Without this fix, the `clean-links` testcase
breaks.

Readability.js

@@ -321,7 +321,7 @@ Readability.prototype = {
       return uri;
     }
 
-    var links = articleContent.getElementsByTagName("a");
+    var links = this._getAllNodesWithTag(articleContent, ["a"]);
     this._forEachNode(links, function(link) {
       var href = link.getAttribute("href");
       if (href) {
@@ -336,7 +336,7 @@ Readability.prototype = {
       }
     });
 
-    var imgs = articleContent.getElementsByTagName("img");
+    var imgs = this._getAllNodesWithTag(articleContent, ["img"]);
     this._forEachNode(imgs, function(img) {
       var src = img.getAttribute("src");
       if (src) {