ncal: correct history section

originally reported Todd C. Miller[0]
Additional data see [1][2].

While here, pet igor.

Closes #152 (github pr)
Sbmitted by: Raf Czlonka

[0]
http://cvsweb.openbsd.org/cgi-bin/cvsweb/src/usr.bin/cal/cal.1?rev=1.28&content-type=text/x-cvsweb-markup
[1] https://www.bell-labs.com/usr/dmr/www/1stEdman.html
[2] https://www.bell-labs.com/usr/dmr/www/man61.pdf