Remove xmlserializer dependency

jsdom can be counted on to do that for us, these days, in a more standards-complaint way. A notable change is that void elements get serialized like <br /> instead of <br/>.

lib/convert.js

@@ -2,7 +2,6 @@
 const path = require("path");
 const fs = require("fs").promises;
 const throat = require("throat");
-const serializeToXML = require("xmlserializer").serializeToString;
 const { JSDOM } = require("jsdom");
 const substitutions = require("./substitutions.json");
 
@@ -139,7 +138,8 @@ function getBodyXML(chapter, contentEl) {
     bodyEl.appendChild(contentEl.firstChild);
   }
 
-  let xml = serializeToXML(bodyEl);
+  const xmlSerializer = new contentEl.ownerDocument.defaultView.XMLSerializer();
+  let xml = xmlSerializer.serializeToString(bodyEl);
 
   // Fix recurring strange pattern of extra <br> in <p>...<em>...<br>\n</em></p>
   xml = xml.replace(/<br \/>\s*<\/em><\/p>/g, "</em></p>");

npm-shrinkwrap.json

@@ -2060,11 +2060,6 @@
       "resolved": "https://registry.npmjs.org/xmlchars/-/xmlchars-2.2.0.tgz",
       "integrity": "sha512-JZnDKK8B0RCDw84FNdDAIpZK+JuJw+s7Lz8nksI7SIuU3UXJJslUthsi+uWBUYOwPFwW7W7PRLRfUKpxjtjFCw=="
     },
-    "xmlserializer": {
-      "version": "0.6.1",
-      "resolved": "https://registry.npmjs.org/xmlserializer/-/xmlserializer-0.6.1.tgz",
-      "integrity": "sha512-FNb0eEqqUUbnuvxuHqNuKH8qCGKqxu+558Zi8UzOoQk8Z9LdvpONK+v7m3gpKVHrk5Aq+0nNLsKxu/6OYh7Umw=="
-    },
     "xtend": {
       "version": "4.0.2",
       "resolved": "https://registry.npmjs.org/xtend/-/xtend-4.0.2.tgz",

package.json

@@ -28,7 +28,6 @@
     "jsdom": "^16.2.2",
     "requisition": "^1.5.0",
     "throat": "^5.0.0",
-    "xmlserializer": "^0.6.1",
     "yargs": "^15.3.1"
   },
   "devDependencies": {