dev.html: Use libsignal from Converse.js CDN

dev.html

@@ -11,7 +11,7 @@
     <link rel="manifest" href="./manifest.json">
     <link rel="shortcut icon" type="image/ico" href="images/favicon.ico"/>
     <link type="text/css" rel="stylesheet" media="screen" href="dist/converse.css" />
-    <script src="3rdparty/libsignal-protocol.js"></script>
+    <script src="https://cdn.conversejs.org/3rdparty/libsignal-protocol.min.js"></script>
     <script src="dist/converse.js"></script>
 </head>