refactor with async/await

Trying to be more robust about error handling and failure.

lib/rand_id.js

@@ -1,11 +1,11 @@
 // all url safe
 // can't use uppercase because hostnames are lowercased
-var chars = 'abcdefghijklmnopqrstuvwxyz';
+const chars = 'abcdefghijklmnopqrstuvwxyz';
 
-module.exports = function rand_id() {
-    var randomstring = '';
+export default function rand_id() {
+    let randomstring = '';
     for (var i=0; i<10; ++i) {
-        var rnum = Math.floor(Math.random() * chars.length);
+        const rnum = Math.floor(Math.random() * chars.length);
         randomstring += chars[rnum];
     }