Escape is needed for some patterns, specifically including dollar marks.

Example:

```
  /dummy/2:
    put:
      summary: "simple"
      responses:
        202:
          description: "accept"
  /dummy/$2:
    put:
      summary: "simple"
      responses:
        202:
          description: "accept"
```

related: https://github.com/aspida/aspida/issues/724 (not the same)