Use regular version of nginx on Arch

`nginx-mainline` requires modules be recompiled each time, and isn't handled automatically. It's still a very new and maintained release.

ansible/files/nginx-docker.conf

@@ -1,9 +1,8 @@
 # {{ ansible_managed }}
 
 server {
-    listen 443 ssl;
-    listen [::]:443 ssl;
-    http2 on;
+    listen 443 ssl http2;
+    listen [::]:443 ssl http2;
 
     server_name {{ server_name }};
     set $upstream {{ upstream }};