Uncaught TypeError: Cannot read property 'postMessageId' of null at onPostMessage (iframe.js:1000)

First of all thank you for awesome library.
When I add component to my form, it throw an error in console:

> Uncaught TypeError: Cannot read property 'postMessageId' of null
at onPostMessage (iframe.js:1000)

here is how I am using it:
```
import ReCAPTCHA from "react-google-recaptcha";

onChange = (value: any) => {
if (value) {
this.setState({ isCaptchaSuccess: true });
}
};

```

Start by reproducing the reported error with the shown ReCAPTCHA component usage and inspect iframe.js around line 1000, especially onPostMessage. Trace why the message handler receives null, then verify that the component renders without the uncaught TypeError and that onChange still receives the CAPTCHA value.

Written by the indexing model from the issue text.