fixed drone

.drone.yml

@@ -28,8 +28,14 @@ name: default
 steps:
     - name: submodules
       image: alpine/git
+      environment:
+          SSH_KEY:
+              from_secret: private_key
       commands:
+          - echo "$SSH_KEY" > $HOME/.ssh/id_rsa
+          - chmod 600 $HOME/.ssh/id_rsa
           - git submodule update --init --recursive
+
     - name: test
       image: docker:latest
       commands: