"-class" doesn't compile as a class but a text

Some CSS framework named their classes like: `-large`, `-big`, `-disabled`,

And when I tried it, it compiled as a text instead of a class.

Tale-Jade:

```
img.-large.-circular
```

Compiled:

```
<img>
  -large.-circular
</img>
```

Expected:

```
<img class="-large -circular">
```
