fix(ci): add tensorflow

.github/workflows/smoketest.yml

@@ -22,7 +22,7 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y ffmpeg
           pip install .
-          pip install .[keras]
+          pip install tensorflow
       - name: Download test resource
         run: |
           curl -o demo.mp4 https://raw.githubusercontent.com/williamfzc/stagesep2-sample/master/videos/demo.mp4