ncurses: upgrade from 6.1 -> 6.1-20181027

This includes fixes for CVE-2018-10754.

While we're changing things, also set the `--with-manpage-format=normal`
configure flag, which prevents the `configure` script from looking in
/usr to determine whether to compress manpages. This was already the
format on NixOS (where these directories don't exist), but making this
explicit makes the build more reproducible on other distros.