The Great Linting Fixes, Drone configuration fix (again) and flatfile changes.

Great linting fixes has been applied, thanks to golangci-lint for
extensive reporting.

Fixed Drone configuration to use array for when-branch statement in
Docker plugin.

Flatfile storage from now will write files with 0600 permission for
greater security.

.drone.yml

@@ -21,7 +21,7 @@ steps:
   - name: docker
     image: plugins/docker
     when:
-      branch: master
+      branch: ["master"]
     settings:
       username:
         from_secret: dockerhub_user