Re-enable remote builds

os/remote-builds/default.nix

@@ -53,6 +53,7 @@ in
                   ControlMaster auto
                   ControlPath ~/.ssh/master-%r@%n:%p
                   ControlPersist 60s
+                  VerifyHostKeyDNS yes
               '') vivariumBuilders
             )
           )
@@ -63,11 +64,11 @@ in
       buildMachines = builtins.map (
         vivariumBuilder: vivariumBuilderDefault // vivariumBuilder
       ) vivariumBuilders;
-      distributedBuilds = false;
+      distributedBuilds = true;
       settings = {
         builders-use-substitutes = true;
         trusted-public-keys = publicKeys;
-        trusted-substituters = builtins.map (
+        substituters = builtins.map (
           builder: "${builder.protocol}://${builder.sshUser}@${builder.hostName}"
         ) config.nix.buildMachines;
       };