Fix Google Storage URLs in input files.

[willsu]

The Google Cloud Storage bucket URL has migrated from gs://broad-references/ to gs://genomics-public-data/references. This PR replaces all references of the old gs:// URL with the new gs:// URL.

The motivation for this change came from some errors received when I was running through the https://cloud.google.com/life-sciences/docs/tutorials/gatk tutorial. This tutorial should be updated to use non-deprecated repositories, but this is an easy fix to correct the Google Storage URLs in the meantime. The tutorial steps ran cleanly after I applied this fix to my local code base.

Thanks for your help and continued maintenance of this repo!

[willsu]

Interesting, it looks like @bshifaw committed a fix just as I was opening this PR. The main difference was that the base URL of gs://gcp-public-data--broad-references was used instead of gs://genomics-public-data/references. I have only tested with the latter, but I did some quick spot checking and it appears that both URLs will work just fine. I'll leave it up to the maintainers to either close this PR or adopt the gs://genomics-public-data/references URL if they prefer.