dnscrypt-proxy service: use up-to-date dnscrypt-resolvers list

The list of public proxies is updated now and again and it's probably a
good idea to always work from the most recent list, rather than the one
that is shipped with the release.  This can be crucial in case of
resolvers that are revealed to have gone rogue or otherwise have been
compromised.

nixos/modules/services/networking/dnscrypt-proxy.nix

@@ -6,7 +6,12 @@ let
   dnscrypt-proxy = pkgs.dnscrypt-proxy;
   cfg = config.services.dnscrypt-proxy;
 
-  resolverListFile = "${dnscrypt-proxy}/share/dnscrypt-proxy/dnscrypt-resolvers.csv";
+  # last updated: 2016-05-04
+  resolverListFile = pkgs.fetchurl {
+    url = "https://raw.githubusercontent.com/jedisct1/dnscrypt-proxy/master/dnscrypt-resolvers.csv";
+    sha256 = "07kbbisrvrqdxif3061hxj3whin3llg4nh50ln7prisi2vbd76xd";
+  };
+
   localAddress = "${cfg.localAddress}:${toString cfg.localPort}";
 
   daemonArgs =