Update faq.html
Update faq.html

AFAIK ExAC is a subset of gnomAD, so I think faq.html is incorrectly specifying the 138k samples of ExAC when it should be referring to gnomAD. I may be wrong ofcourse.
macarthur-lab/gnomad_browser,macarthur-lab/gnomad_browser,macarthur-lab/gnomad_browser,macarthur-lab/gnomad_browser,macarthur-lab/gnomad_browser