fix(users): use updateAsync for Meteor 3 server-side user writes

Meteor.users.update() is sync-only and no longer exists server-side
under Meteor 3, so it threw on every call, surfacing as a generic
500 to the client. users.setLang runs on every page load for logged-in
users, which is what broke /zones; the same bug in edit-profile.js
was silently breaking /profile too.

imports/api/Users/server/methods.js

@@ -33,9 +33,9 @@ Meteor.methods({
         throw new Meteor.Error('500', exception);
       });
   },
-  'users.setLang': function userLang(lang) {
+  'users.setLang': async function userLang(lang) {
     check(lang, validLangCode);
-    Meteor.users.update({ _id: this.userId }, { $set: { lang } });
+    await Meteor.users.updateAsync({ _id: this.userId }, { $set: { lang } });
   },
   'auth.getHash': async function getHash() {
     const token = Accounts._generateStampedLoginToken();