Scale up wiki to CPX21 (fixes #249)

The wiki box was a little small and actually ran out of RAM in some cases.

tf-stage1/archlinux.tf

@@ -126,7 +126,7 @@ locals {
       domain      = "svn2gittest"
     }
     "wiki.archlinux.org" = {
-      server_type = "cpx11"
+      server_type = "cpx21"
       domain      = "wiki"
       ttl         = 600
     }