fix: Client#generateInvite resolving permissions incorrectly

src/client/Client.js

@@ -391,20 +391,15 @@ class Client extends EventEmitter {
   /**
    * Generates a link that can be used to invite the bot to a guild.
    * <warn>This is only available when using a bot account.</warn>
-   * @param {PermissionResolvable[]|number} [permissions] Permissions to request
+   * @param {PermissionResolvable|PermissionResolvable[]} [permissions] Permissions to request
    * @returns {Promise<string>}
    * @example
    * client.generateInvite(['SEND_MESSAGES', 'MANAGE_GUILD', 'MENTION_EVERYONE'])
-   *   .then(link => {
-   *     console.log(`Generated bot invite link: ${link}`);
-   *   });
+   *   .then(link => console.log(`Generated bot invite link: ${link}`))
+   *   .catch(console.error);
    */
   generateInvite(permissions) {
-    if (permissions) {
-      if (permissions instanceof Array) permissions = Permissions.resolve(permissions);
-    } else {
-      permissions = 0;
-    }
+    permissions = typeof permissions === 'undefined' ? 0 : Permissions.resolve(permissions);
     return this.fetchApplication().then(application =>
       `https://discordapp.com/oauth2/authorize?client_id=${application.id}&permissions=${permissions}&scope=bot`
     );