Fix max_concurrency (#7)

Author: Brainicism

lib/Client.js

@@ -359,6 +359,8 @@ class Client extends EventEmitter {
     async connect() {
         try {
             const data = await (this.options.maxShards === "auto" ? this.getBotGateway() : this.getGateway());
+            this.shards.maxConcurrency = this.options.maxShards === "auto" ? data.session_start_limit.max_concurrency : 1;
+            this._client.options.useMaxConcurrency = this._client.options.useMaxConcurrency && this.shards.maxConcurrency !== 1;
             if(!data.url || (this.options.maxShards === "auto" && !data.shards)) {
                 throw new Error("Invalid response from gateway REST call");
             }