Update webscanner

[F3licity]

There are some links that Webscanner did not report. Need to debug though whether the issue lies on the webscanner or on GItbook.
Here are some broken links reported by another tool:

Another interesting tool:
https://github.com/scivision/linkchecker-markdown

[F3licity]

We could check only the parent link on external domains to see if we get a 200 and if yes, to not follow them deeper.