Short-term fix for jade@1.0.0 breaking changes

jade 1.0.0 breaks groc:

```
Warning: Jade:1
  > 1| !!! 5
    2| html(lang="en")
    3|   head
    4|     title= pageTitle
`!!!` is deprecated, you must now use `doctype`
```

Unfortunately, because the dependency is specified as "jade": ">= 0.17.0" in the package.json, any new or updated installations are broken right now. This small change will fix them until groc is compatible with jade@1.0.0.