allow users and members to not be cached (#1097)

src/structures/Guild.js

@@ -325,14 +325,15 @@ class Guild {
   /**
    * Fetch a single guild member from a user.
    * @param {UserResolvable} user The user to fetch the member for
+   * @param {boolean} [cache=true] Insert the user into the users cache
    * @returns {Promise<GuildMember>}
    */
-  fetchMember(user) {
+  fetchMember(user, cache = true) {
     if (this._fetchWaiter) return Promise.reject(new Error('Already fetching guild members.'));
     user = this.client.resolver.resolveUser(user);
     if (!user) return Promise.reject(new Error('User is not cached. Use Client.fetchUser first.'));
     if (this.members.has(user.id)) return Promise.resolve(this.members.get(user.id));
-    return this.client.rest.methods.getGuildMember(this, user);
+    return this.client.rest.methods.getGuildMember(this, user, cache);
   }
 
   /**