fix requirements (#1085)

requirements.txt

 bce-python-sdk
-flake8 >= 3.7.9
 flask >= 1.1.1
 Flask-Babel >= 1.0.0
 numpy
 Pillow >= 7.0.0
-pre-commit
 protobuf >= 3.11.0
 requests
-shellcheck-py
 six >= 1.14.0
 matplotlib
-pandas
+pandas
\ No newline at end of file