update GWAS genetic association references

[andrewsu]

Currently we have many genetic associations (P2293) that link genes to diseases. For example, GSDMA (Q18054256) has genetic association to [asthma (Q35869)]:(https://www.wikidata.org/wiki/Q35869). Very often these genetic associations list genome.gov/gwastudies in the reference URLs:

But https://www.genome.gov/gwastudies now redirects to https://www.ebi.ac.uk/gwas/. We should update those reference URL links (and ideally update the data too). Links to http://www.genome.gov/gwastudies/index.cfm?gene=GSDMA, for example, should be updated to https://www.ebi.ac.uk/gwas/genes/GSDMA