Update python-app.yml

自动构建

.github/workflows/python-app.yml

@@ -27,7 +27,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install flake8 pytest
-        if exist requirements.txt: (pip install -r requirements.txt)
+        if (exist requirements.txt): (pip install -r requirements.txt)
     - name: Lint with flake8
       run: |
         # stop the build if there are Python syntax errors or undefined names