Update README.md (#79)

fixed AsyncWiFiManagerParameter instead of wifimanagerparameter

README.md

@@ -194,13 +194,13 @@ Usage scenario would be:
 - add the custom parameters to WiFiManager using
  ```cpp
  // id/name, placeholder/prompt, default, length
- WiFiManagerParameter custom_mqtt_server("server", "mqtt server", mqtt_server, 40);
+ AsyncWiFiManagerParameter custom_mqtt_server("server", "mqtt server", mqtt_server, 40);
  wifiManager.addParameter(&custom_mqtt_server);
 
  ```
 - if connection to AP fails, configuration portal starts and you can set /change the values (or use on demand configuration portal)
 - once configuration is done and connection is established [save config callback]() is called
-- once WiFiManager returns control to your application, read and save the new values using the `WiFiManagerParameter` object.
+- once WiFiManager returns control to your application, read and save the new values using the `AsyncWiFiManagerParameter` object.
  ```cpp
  mqtt_server = custom_mqtt_server.getValue();
  ```