Moderate vulnerability in `marked` dependency

I found that the project has a moderate vulnerability with one of the dependencies : 

```
  Moderate        Regular Expression Denial of Service

  Package         marked

  Patched in      >=0.6.2

  Dependency of   stylemark [dev]

  Path            stylemark > marked

  More info       https://npmjs.com/advisories/812
```

I can make a PR if you like.