
NetCDF-4.8.1 has been released. As discussed in https://github.com/Unidata/netcdf-c/issues/2110 (netcdf-c-4.8.1.tar.gz not on ftp site... #2110), the canonical download site for netCDF releases has been changed and the previous ftp site is no longer available. This PR updates the `url` to point to the new recommended download site and updates the sha256 checksums for the new tar files.