fix(ThreadMemberManager): fix ThreadMemberManager#add and ThreadMembe…

…rManager#fetch (#5927)

src/managers/ThreadMemberManager.js

@@ -77,7 +77,7 @@ class ThreadMemberManager extends BaseManager {
     const id = member === '@me' ? member : this.client.users.resolveID(member);
     if (!id) return Promise.reject(new TypeError('INVALID_TYPE', 'member', 'UserResolvable'));
     return this.client.api
-      .channels(this.id, 'thread-members', id)
+      .channels(this.thread.id, 'thread-members', id)
       .put({ reason })
       .then(() => id);
   }
@@ -103,7 +103,7 @@ class ThreadMemberManager extends BaseManager {
   async fetch(cache = true) {
     const raw = await this.client.api.channels(this.thread.id, 'thread-members').get();
     return raw.reduce((col, rawMember) => {
-      const member = this.add(rawMember, cache);
+      const member = this._add(rawMember, cache);
       return col.set(member.id, member);
     }, new Collection());
   }