Replace WordPress <img>s with emoji

Noticed via the validation discussed in #22, which was failing on the draggable attribute.

lib/convert-worker.js

@@ -243,6 +243,12 @@ function getBodyXML(chapter, book, contentEl) {
   xml = xml.replace(/ ? <\/p>/g, "</p>");
   xml = xml.replace(/([a-z]) ,/g, "$1,");
 
+  // Use actual emojis instead of images
+  xml = xml.replace(
+    // eslint-disable-next-line max-len
+    /<img width="16" height="16" class="wp-smiley emoji" draggable="false" alt="O_o" src="https:\/\/s1.wp.com\/wp-content\/mu-plugins\/wpcom-smileys\/o_O.svg" style="height: 1em; max-height: 1em;" \/>/g,
+    "🤨");
+
   xml = fixTruncatedWords(xml);
   xml = fixDialogueTags(xml);
   xml = fixForeignNames(xml);