CI: maybe fix docker build

.drone.yml

@@ -12,9 +12,24 @@ steps:
   commands:
   - test -z $(gofmt -l .)
 - name: build
-  image: docker
+  image: docker:dind
+  volumes:
+  - name: dockersock
+    path: /var/run
   commands:
   - docker build -f Dockerfile .
+
+services:
+- name: docker
+  image: docker:dind
+  privileged: true
+  volumes:
+  - name: dockersock
+    path: /var/run
+
+volumes:
+- name: dockersock
+  temp: {}
 ---
 kind: pipeline
 type: kubernetes