Binary tree visualization in <pre> tag inproperly trimmed

## 🐛 Bug Report

![image](https://user-images.githubusercontent.com/20227484/57236931-a9388f80-7058-11e9-8ff4-130b977772e0.png)

Reason:
```ts
body: body.join("\n").replace(/<pre>\s*([^]+?)\s*<\/pre>/g, "<pre><code>$1</code></pre>"),
```
The `<pre>\s*` reduces all the white spaces. In fact, only `\r\n` is needed to not be caught.