fix workflow

Author: yosupo06

.github/workflows/document.yml

@@ -8,7 +8,9 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v2
-
+      - name: Set branch name
+        id: branch
+        run: echo "::set-output name=BRANCH_NAME::${GITHUB_REF##*/}"
       - name: Set up Python 3.7
         uses: actions/setup-python@v2
         with:
@@ -30,4 +32,4 @@ jobs:
         with:
           deploy_key: ${{ secrets.ACTIONS_DEPLOY_KEY }}
           publish_dir: ./tools/generated
-          destination_dir: ${GITHUB_REF##*/}
+          destination_dir: ${( steps.branch.outputs.BRANCH_NAME )}