Update users.yaml
Update users.yaml

Consolidating separate entries for 'Michelle Gwinn' and 'Michelle Giglio' into one. Added "xref: 'GOC:mlg'" into Giglio entry and deleted Gwinn entry.
geneontology/go-site,geneontology/go-site,geneontology/go-site,geneontology/go-site,geneontology/go-site