fix: secrets' name

Author: crossfw

.github/workflows/docker.yml

@@ -27,8 +27,8 @@ jobs:
         name: Login to DockerHub
         uses: docker/login-action@v1
         with:
-          username: ${{ secrets.DOCKER_USERNAME }}
-          password: ${{ secrets.DOCKER_PASSWORD }}
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_PASSWORD }}
       -
         name: Build and push
         uses: docker/build-push-action@v2