onOpen not working

Trying to be called when the user opens the modal, using ReactJs:

```
class Test extends React.component {

handleOpen = () => {
alert("User opened...");
}

render = () => {
return ();

}
export default Test;
```

The `handleOpen` is never called.

Version:

```
$ npm view react-datetime

react-datetime@3.0.4 | MIT | deps: 1 | versions: 78
A lightweight but complete datetime picker React.js component
https://github.com/arqex/react-datetime

keywords: react, react-component, datepicker, timepicker, datetimepicker, datetime

dist
.tarball: https://registry.npmjs.org/react-datetime/-/react-datetime-3.0.4.tgz
.shasum: 176159d08d35c9e750f0be2f0b974e4f9532ffa5
.integrity: sha512-v6MVwCve+DRaLN2f22LTO5TlrPpkUXumPkp1zfrbhaFtSYGl2grZ2JtwJfLxRj/T4ACyePAV4srCR6cMSiQ/Iw==
.unpackedSize: 295.5 kB

dependencies:
prop-types: ^15.5.7

maintainers:
- arqex
- simeg
- layneanderson

dist-tags:
alpha: 3.0.0-alpha.5 beta: 3.0.0-beta.8 latest: 3.0.4

published 2 months ago by arqex

```

Start by tracing how the DateTime component handles the onOpen prop and reproduce the report with the provided React example on version 3.0.4. Done means the supplied handleOpen callback runs when the user opens the modal, with coverage for that behavior if the project’s existing tests support it.

Written by the indexing model from the issue text.