Updated HGNC download link (issue #506)

[mialaalv]

The previous link is no longer working. All download files including the archive files are now in a publicly accessible Google Storage Bucket. New link found at https://www.genenames.org/download/statistics-and-files/

PR checklist

• This comment contains a description of changes (with reason).
• If you've fixed a bug or added code that should be tested, add tests!
• If you've added a new tool - have you followed the pipeline conventions in the contribution docs
• If necessary, also make a PR on the nf-core/rnafusion branch on the nf-core/test-datasets repository.
• Make sure your code lints (nf-core lint).

• Check for unexpected warnings in debug mode (nextflow run . -profile debug,test,docker --outdir <OUTDIR>).
• Usage Documentation in docs/usage.md is updated.
• Output Documentation in docs/output.md is updated.
• CHANGELOG.md is updated.
• README.md is updated (including new tool citations and authors/contributors).