Added 3-by-4 ratio linux calendars for printing on 18x24 paper.

8 lat temu · a1e1981777
--- a/calendars/2018/eu/hexadecimal-linux-2018-black-18-by-24.png
+++ b/calendars/2018/eu/hexadecimal-linux-2018-black-18-by-24.png
--- a/calendars/2018/eu/hexadecimal-linux-2018-white-18-by-24.png
+++ b/calendars/2018/eu/hexadecimal-linux-2018-white-18-by-24.png