Security vulnerability in js-yaml

GitHub raise a security alert when using the last version of rollup-plugin-postcss:

>**1 js-yaml vulnerability found in package-lock.json**
>
>Remediation
>Upgrade js-yaml to version 3.13.1 or later. For example:
>```
>"dependencies": {
> "js-yaml": ">=3.13.1"
>}
>```
>or…
>```
>"devDependencies": {
> "js-yaml": ">=3.13.1"
>}
>```

I found out that rollup-plugin-postcss uses cssnano, which uses cosmiconfig, which uses js-yaml.
cosmiconfig and cssnano already updated their dependencies to fix the security alert, so you just need to update your dependency to **cssnano 4.1.10**