Update OpenBSD download link

old link was dead / the site shut down

See discussion on dlang/dub#2592 (comment)

Author: WebFreak001

download.dd

@@ -174,7 +174,7 @@ sudo snap install --classic dub
 \# install LDC compiler with LLVM backend
 sudo snap install --classic ldc2))
 
-$(DOWNLOAD_OTHER $(OPENBSD), $(LINK2 https://openports.se/lang/dmd, OpenBSD), $(CONSOLE # install DMD compiler
+$(DOWNLOAD_OTHER $(OPENBSD), $(LINK2 https://openports.pl/path/lang/dmd, OpenBSD), $(CONSOLE # install DMD compiler
 doas pkg_add dmd
 
 \# install DUB package/build manager (and DMD if not already installed)