I can’t comment on why it’s not updated yet on the download page; I’d guess it’s just a manual step for someone that hasn’t been done yet. I do notice that if you change the ‘2’ to a ‘3’ in the download link for 1.8.2 then out comes a dmg file 
:
https://julialang-s3.julialang.org/bin/mac/x64/1.8/julia-1.8.3-mac64.dmg