Update to 0.20

Upstream changes:
0.20

2019-04-16  Sam Varshavchik  <mrsam@courier-mta.com>

        * _ipcmp: handle comparison of mixed IPv4 and IPv6-specified
        addresses, allowing cidrlookup() to look up IPv6-mapped IPv4 addresses
        in IPv4 address ranges, and vice versa.

(wen)