Update Hugo example for v7

[markdumay]

Is your feature request related to a problem? Please describe.
The Hugo guide provides a clear example of how to use PurgeCSS with Hugo. However, the example is no longer compatible with v7.0.2, which introduced a breaking change in how to import the module.

Describe the solution you'd like
Update the Hugo example to be compatible with PurgeCSS v7.

Describe alternatives you've considered
I've tried to update the module configuration myself, but I was struggling to get it to work with Hugo. Any help is much appreciated.

Additional context
N/A