alpine: make nginx user home dir consistent with debian and rpm packaging.

alpine/nginx.pre-install

diff --git a/alpine/nginx.pre-install b/alpine/nginx.pre-install
index cbb627d..31f5e2a 100644
--- a/alpine/nginx.pre-install
+++ b/alpine/nginx.pre-install
@@ -12,7 +12,7 @@
 
 if ! getent passwd nginx >/dev/null; then
     adduser -SDH \
-	-h /var/lib/nginx \
+	-h /var/cache/nginx \
 	-s /sbin/nologin \
 	-G nginx \
 	-g nginx \