update drone syntax for 1.x

.drone.yml

-pipeline:
-  lint-charts:
+---
+kind: pipeline
+name: default
+
+platform:
+  os: linux
+  arch: amd64
+
+steps:
+- name: lint-charts
+  pull: default
   image: guangbo/chart-testing:v2.0.2-rancher1
   commands:
   - git remote add rancher-charts https://github.com/rancher/charts