Remove unnecessary array conversions

src/client/Client.js

@@ -251,13 +251,13 @@ class Client extends EventEmitter {
   /**
    * This shouldn't really be necessary to most developers as it is automatically invoked every 30 seconds, however
    * if you wish to force a sync of Guild data, you can use this. Only applicable to user accounts.
-   * @param {Guild[]} [guilds=this.guilds.array()] An array of guilds to sync
+   * @param {Guild[]|Collection<string, Guild>} [guilds=this.guilds] An array or collection of guilds to sync
    */
-  syncGuilds(guilds = this.guilds.array()) {
+  syncGuilds(guilds = this.guilds) {
     if (!this.user.bot) {
       this.ws.send({
         op: 12,
-        d: guilds.map(g => g.id),
+        d: guilds instanceof Collection ? guilds.keyArray() : guilds.map(g => g.id),
       });
     }
   }