pin markupsafe to 2.0.1

hitting this issue  and looks like latest update to markupsafe has removed soft_unicode, pinning markupsafe to 2.0.1 in requirements.txt fixes the issue

```
ImportError: cannot import name 'soft_unicode' from 'markupsafe' (/home/vasu/venv/lib/python3.8/site-packages/markupsafe/__init__.py)
```
https://github.com/aws/aws-sam-cli/issues/3661