try docker login in dind

.drone.yml

@@ -5,14 +5,14 @@ name: build_lektor
 
 steps:
   - name: env
-    image: busybox
+    image: dind
     environment:
       DOCKER_USERNAME:
         from_secret: "docker_username"
       DOCKER_PASSWORD:
         from_secret: "docker_password"
     commands:
-      - env
+      - docker login -u ${DOCKER_USERNAME} -p ${DOCKER_PASSWORD}
   - name: build
     image: plugins/docker
     settings: