Use new cmd for nix builds

.drone.yml

@@ -28,7 +28,10 @@ steps:
     - name: deps
       path: /nix/store
   commands:
-    - nix-build --argstr version ${DRONE_TAG} --argstr rev ${DRONE_COMMIT} .#image
+    - mkdir /root/.ssh
+    - echo "${DRONE_SSH_KEY}" > /root/.ssh/id_ed25519
+    - echo "${GIT_C3C_KNOW_HOSTS}" > /root/.ssh/known_hosts
+    - nix --extra-experimental-features nix-command --extra-experimental-features flakes build .#image
 
 - name: publish
   image: docker:dind
@@ -87,6 +90,6 @@ services:
 
 ---
 kind: signature
-hmac: df9a2fb07428f545bc41b36d4c8b53e0e7223333f614e2d5d890a1adbd7f324b
+hmac: b94e2da88e7b30ba6eef9ebc27e715aab856c4fdcc142bbbb9f7352e0421714e
 
 ...