DocumentTitle is undefined when running tests

When using this library with TypeScript, I am encountering errors when running tests:

```typescript
import DocumentTitle from 'react-document-title';

// ...

renderToString(



);
```

My typings file:
```typescript
// @types/react-document-title.d.ts

declare module 'react-document-title' {
import * as React from 'react';

interface DocumentTitleProps {
title: string;
}

export default class DocumentTitle extends React.Component {
public static rewind(): string;
public static peek(): string;
}
}

```

This code runs perfectly fine when executed on the server, but during testing it fails:

`Invariant Violation: Element type is invalid: expected a string (for built-in components) or a class/function (for composite components) but got: undefined. You likely forgot to export your component from the file it's defined in, or you might have mixed up default and named imports.
`

Debugging shows that the import of `react-document-title` simply returns `undefined` when using jest, but the proper class when running the server.

Does anybody know what might be the cause of this?