Fix #2673. Make nginx root /usr/share/nginx/html
Fix #2673. Make nginx root /usr/share/nginx/html

mkeilman/sirepo,radiasoft/sirepo,radiasoft/sirepo,mkeilman/sirepo,mkeilman/sirepo,mkeilman/sirepo,radiasoft/sirepo,radiasoft/sirepo,radiasoft/sirepo