marko run static $slug bug

Building this repo results in the following dist:

dist
├── $
│   └── index.html
├── 404
│   └── index.html
├── path
│   └── index.html
└── index.html

But it should be:

dist
├── 404
│   └── index.html
├── path
│   └── index.html
└── index.html