3.1.1

• The vendored libmaxminddb has been updated to 1.13.3. This includes
  a fix for the validation of empty maps and arrays at the end of the
  metadata section. Previously, the extension would incorrectly reject
  databases where a 0-element map or array was the last field in metadata.
  Reported in vimt/MaxMind-DB-Writer-python#16.