Fix Docker credential secrets

.github/workflows/docker.yml

@@ -29,8 +29,8 @@ jobs:
       - name: Docker Hub Description
         uses: peter-evans/dockerhub-description@v3
         with:
-          username: ${{ secrets.DOCKERHUB_USERNAME }}
-          password: ${{ secrets.DOCKERHUB_PASSWORD }}
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_PASSWORD }}
           repository: libreddit/libreddit
       - name: Build and push
         uses: docker/build-push-action@v2