feat: update (see description)

- Remove `bignumber.js`
- Fix `circular dependency`
- Fix: missing activity.name (SpotifyRPC)
- Refactor code
- Update UserAgent

src/structures/DMChannel.js

@@ -257,10 +257,6 @@ class DMChannel extends Channel {
       this.client.voice.adapters.set(this.id, methods);
       return {
         sendPayload: data => {
-          data.d = {
-            ...data.d,
-            self_video: false,
-          };
           if (this.shard.status !== Status.READY) return false;
           this.shard.send(data);
           return true;