Newline removed before <pre>



```go
package main

import (
	"fmt"

	"github.com/yosssi/gohtml"
)

func main() {
	h := `<h1>Pre</h1>
	
<pre>some code</pre>

<h1>Post</h1>
`
	fmt.Println(gohtml.Format(h))
}

```

Prints

```bash
<h1>
  Pre
</h1><pre>some code</pre>
<h1>
  Post
</h1>
```

I understand the need for whitespace-preservation **inside** pre, but the above looks wrong to me.
