Fix stylelint dependencies

[NickDJM]

As per #11 having stylelint as a direct dependency can cause issues if the project falls out of date with the current version of stylelint.

I've refactored the code to mimic the route that the official eslint plugin has gone.

Using @vue/cli-shared-utils we can load the user's version of stylelint with our included version as a fallback.

I've also did an npm audit fix to resolve some of the critical vulnerabilities.

[dukhevych]

Would be great to merge this.

[ralbach]

This would be great, especially if we could bump stylelint up to 14.0.0 to reduce security concerns from dependencies.