fix(GuildMemberManager): nick endpoint (#7151)

Author: muchnameless

src/managers/GuildMemberManager.js

@@ -268,7 +268,7 @@ class GuildMemberManager extends CachedManager {
 
     let endpoint = this.client.api.guilds(this.guild.id);
     if (id === this.client.user.id) {
-      const keys = Object.keys(_data);
+      const keys = Object.keys(data);
       if (keys.length === 1 && keys[0] === 'nick') endpoint = endpoint.members('@me');
       else endpoint = endpoint.members(id);
     } else {