Nested selectors are loosing dollar sign

__Expected behavior:__
Normal selector nesting

__Describe the bug:__
When nesting a selector with a dollar sign, it disappears

__Codesandbox link:__
[https://codesandbox.io/s/react-jss-playground-j9toj](https://codesandbox.io/s/react-jss-playground-j9toj)

There I've just added:
```javascript
"& h1": {
color: "red"
}
```
And changed `Comp` to `Comp$1`

And look at the ``:
```css
.Comp\$1-wrapper-0-1-13 {
padding: 40px;
background: #f7df1e;
text-align: left;
}
.Comp\1-wrapper-0-1-13 h1 {
color: red;
}
```

__Versions:__
- react-jss: 8.6.1
- Browser: Safari 12.1.2
- OS: macOS 10.14.6