Npgsql 3.1.1 has been released and is available on nuget.org.
This releases fixes some minor bugs and removes an embarrassing Console.WriteLine that somehow made it into the final release.
It also implements the new CoreCLR data reader schema API (https://github.com/dotnet/corefx/issues/5915), a better way to discover information about columns you select. It's been made available in .NET Framework as well.
The complete list of issues is here.