pages:deploy step was failing with the following error:

```
unitialized constant SafeZip::Extract::Zip
```

Since license_finder already pulls in rubyzip, we can make it
a required gem. We also use the scope operator to make the reference to
Zip::File explicit.

RubyZip allows us to perform strong validation of
expanded paths where we do extract file.

We introduce the following additional checks
to extract routines:

1. None of path components can be symlinked,
2. We drop privileges support for directories,
3. Symlink source needs to point within the target directory,
   like `public/`,
4. The symlink source needs to exist ahead of time.