NodeMCU DHT11 ThingSpeak Upload

#include <DHT.h>  // Including library for dht
#include <ESP8266WiFi.h>
String apiKey = "Your ThingSpeak Write API Key";     //  Enter your Write API key from ThingSpeak
const char *ssid =  "WiFi Name";     // replace with your wifi ssid and wpa2 key
const char *pass =  "WiFi Password";
const char* server = "api.thingspeak.com";
#define DHTPIN 13          //D7 pin where the dht11 is connected
DHT dht(DHTPIN, DHT11);
WiFiClient client;
void setup() {
     Serial.begin(115200);
     delay(10);
     dht.begin();
     Serial.println("Connecting to ");
     Serial.println(ssid);
     WiFi.begin(ssid, pass);
     while (WiFi.status() != WL_CONNECTED)
     {
            delay(500);
            Serial.print(".");
     }
      Serial.println("");
      Serial.println("WiFi connected");

}

void loop()
{

      float h = dht.readHumidity();
      float t = dht.readTemperature();

              if (isnan(h) || isnan(t))
                 {
                     Serial.println("Failed to read from DHT sensor!");
                      return;
                 }

                         if (client.connect(server,80))   //   "184.106.153.149" or api.thingspeak.com
                      {

                             String postStr = apiKey;
                             postStr +="&field1=";
                             postStr += String(t);
                             postStr +="&field2=";
                             postStr += String(h);
                             postStr += "\r\n\r\n";

                             client.print("POST /update HTTP/1.1\n");
                             client.print("Host: api.thingspeak.com\n");
                             client.print("Connection: close\n");
                             client.print("X-THINGSPEAKAPIKEY: "+apiKey+"\n");
                             client.print("Content-Type: application/x-www-form-urlencoded\n");
                             client.print("Content-Length: ");
                             client.print(postStr.length());
                             client.print("\n\n");
                             client.print(postStr);

                             Serial.print("Temperature: ");
                             Serial.print(t);
                             Serial.print(" degrees Celsius, Humidity: ");
                             Serial.print(h);
                             Serial.println("%. Send to Thingspeak.");
                        }
          client.stop();

          Serial.println("Waiting...");

  // thingspeak needs minimum 15 sec delay between updates, i've set it to 30 seconds
  delay(15000);
}