`filter_versions` default in `build_documentation` should be `last ∘ sort`

It doesn't look like `package.versions` is guaranteed to be sorted, and I presume the intent here is to pick the latest version?

https://github.com/JuliaDocs/DocumentationGenerator.jl/blob/80b8c217a193a283c1617157c6a6e343fb8ecb79/src/DocumentationGenerator.jl#L80