我正在嘗試在 aws ec2（ubuntu 18.04）上設(shè)置 apache 氣流Python 版本：3.6.9 點子版本：9.0.1要安裝 Apache Airflow，我使用了以下命令。pip3 install apache-airflow[postgres,celery,rabbitmq,ldap,crypto,aws]當(dāng)我執(zhí)行airflow initdb它時顯示錯誤  File "/home/ubuntu/.local/bin/airflow", line 26, in <module>    from airflow.bin.cli import CLIFactory  File "/home/ubuntu/.local/lib/python3.6/site-packages/airflow/bin/cli.py", line 71, in <module>    from airflow.www_rbac.app import cached_app as cached_app_rbac  File "/home/ubuntu/.local/lib/python3.6/site-packages/airflow/www_rbac/app.py", line 28, in <module>    from flask_appbuilder import AppBuilder, SQLA  File "/home/ubuntu/.local/lib/python3.6/site-packages/flask_appbuilder/__init__.py", line 6, in <module>    from .base import AppBuilder  # noqa: F401  File "/home/ubuntu/.local/lib/python3.6/site-packages/flask_appbuilder/base.py", line 8, in <module>    from .api.manager import OpenApiManager  File "/home/ubuntu/.local/lib/python3.6/site-packages/flask_appbuilder/api/manager.py", line 7, in <module>    from flask_appbuilder.baseviews import BaseView  File "/home/ubuntu/.local/lib/python3.6/site-packages/flask_appbuilder/baseviews.py", line 21, in <module>    from .forms import GeneralModelConverter  File "/home/ubuntu/.local/lib/python3.6/site-packages/flask_appbuilder/forms.py", line 17, in <module>    from .fieldwidgets import (  File "/home/ubuntu/.local/lib/python3.6/site-packages/flask_appbuilder/fieldwidgets.py", line 3, in <module>    from wtforms.widgets import html_params, HTMLStringImportError: cannot import name 'HTMLString'有人可以幫我嗎？