Fix the version of isort (#385)

.github/workflows/build.yml

@@ -15,11 +15,11 @@ jobs:
       - name: Install linting dependencies
         run: |
           python -m pip install --upgrade pip
-          pip install flake8 isort yapf
+          pip install flake8 yapf isort==4.3.21
       - name: Lint with flake8
         run: flake8 --max-complexity 20 .
       - name: Lint with isort
-        run: isort -rc --check-only --diff mmcv/ tests/ examples/
+        run: isort --recursive --check-only --diff mmcv/ tests/ examples/
       - name: Format python codes with yapf
         run: yapf -r -d mmcv/ tests/ examples/
       - name: Format c/cuda codes with clang-format