Fixed syntax for sendSDKMessage example

[Julix91]

Fixed a syntax issue.

Double checked that it shouldn't take a function as argument, and confirmed:

sendSDKMessage(data) {
    if (!this.loaded) {
      return; // Not loaded.
    } 

    this.embed.contentWindow.postMessage({ 
      type: _eventNames.SEND_SDK_MESSAGE,
      value: data,
    }, _furioosServerUrl);
  }