Add auto build for shellcheck image

.drone.yml

@@ -2,7 +2,7 @@ kind: pipeline
 name: default
 
 steps:
-- name: docker
+- name: build gbp
   image: plugins/docker
   settings:
     username:
@@ -12,3 +12,14 @@ steps:
     dockerfile: gbp/Dockerfile
     repo: evolix/gbp
     tags: latest
+
+- name: build shellcheck
+  image: plugins/docker
+  settings:
+    username:
+      from_secret: docker_username
+    password:
+      from_secret: docker_password
+    dockerfile: shellcheck/Dockerfile
+    repo: evolix/shellcheck
+    tags: latest