Added kaniko secret specification

.drone.yml

@@ -31,7 +31,11 @@ steps:
 
   - name: build and push
     image: gcr.io/kaniko-project/executor:latest
+    environment:
+      DOCKER_CONFIG: /drone/src/.docker
     commands:
+      - mkdir -p /drone/src/.docker
+      - echo $DOCKER_CONFIG_SECRET > /drone/src/.docker/config.json
       - /kaniko/executor 
         --context=. 
         --dockerfile=Dockerfile