TypeError when GitHub URL is not defined

[aalykiot]

When a module does not specify a GitHub URL it causes npcheck to crash with the following error:

TypeError: Cannot read property 'url' of undefined
    at archivePlugin (/Users/alex/Workspace/repos/redhat/npcheck/src/plugins/archive.js:6:39)
    at Object.run (/Users/alex/Workspace/repos/redhat/npcheck/src/cli.js:94:30)
    at processTicksAndRejections (node:internal/process/task_queues:94:5)

We should probably return a warning as a result when GitHub URL is not defined