JSX renderer renders self closing tags wrong

Just noticed, that the jsx renderer double closes self closing tags like `meta` or `base`.

Test case:
```jsx
const render = require("preact-render-to-string/jsx");

const html = <html><head><base href="foo/" /></head></html>;
console.log(render(html));
// Logs:
// <html>
//   <head>
//     <base href="foo/" /></base>
//   </head>
// </html>
```