Makefile: when deploying the website, avoid setting timestamps & owners

The current setup on our webserver disallows setting timestamps or
permissions on the root (of the website) directory, so `rsync -a`
caused an error.

`-a` is a synonym of `-rlptgoD`; the new options are that minus `-t` for
setting times, `-o` and `-g` for setting file ownership (they should
be owned by the uploading user), and `-p` for setting permissions.

Makefile

@@ -233,7 +233,7 @@ project-website:
 	cd web/project-website; hugo --baseURL https://flamenco.blender.org/
 	rsync web/project-website/public/ ${WEBSERVER_SSH}:${WEBSERVER_ROOT}/ \
 		-e "ssh" \
-		-a \
+		-rl \
 		--exclude v2/ \
 		--exclude downloads/ \
 		--exclude .well-known/ \