[skip ci] enable set-env

https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

.github/workflows/dockerhub.yml

@@ -4,6 +4,8 @@ on:
     types: [published]
 jobs:
   update:
+    env:
+      ACTIONS_ALLOW_UNSECURE_COMMANDS: true
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master