update drone

.drone.yml

@@ -0,0 +1,16 @@
+kind: pipeline
+name: default
+
+steps:
+- name: docker
+  image: plugins/docker
+  settings:
+    username: 
+      from_secret: docker_username
+    password:
+      from_secret: docker_password
+    repo: lizheming/drone-coveralls
+    when:
+      event: tag
+    branches:
+      - master