text: Title: On mac, flask fab create-app fails until to deactivate / reactivate the venv
  Body: If you'd like to report a bug in Flask-Appbuilder, fill out the template below. Provide
  any extra information that may be useful
  
  Responsible disclosure:
  We want to keep Flask-AppBuilder safe for everyone. If you've discovered a security vulnerability
  please report to danielvazgaspar@gmail.com.
  
  ### Environment
  
  Flask-Appbuilder version: 3.4.4
  
  pip freeze output:
  
  apispec==3.3.2
  attrs==21.4.0
  Babel==2.9.1
  click==7.1.2
  colorama==0.4.4
  defusedxml==0.7.1
  dnspython==2.2.0
  email-validator==1.1.3
  Flask==1.1.4
  Flask-AppBuilder==3.4.4
  Flask-Babel==2.0.0
  Flask-JWT-Extended==3.25.1
  Flask-Login==0.4.1
  Flask-OpenID==1.3.0
  Flask-SQLAlchemy==2.5.1
  Flask-WTF==0.14.3
  greenlet==1.1.2
  idna==3.3
  itsdangerous==1.1.0
  Jinja2==2.11.3
  jsonschema==4.4.0
  MarkupSafe==2.0.1
  marshmallow==3.14.1
  marshmallow-enum==1.5.1
  marshmallow-sqlalchemy==0.26.1
  prison==0.2.1
  PyJWT==1.7.1
  pyrsistent==0.18.1
  python-dateutil==2.8.2
  python3-openid==3.2.0
  pytz==2021.3
  PyYAML==6.0
  six==1.16.0
  SQLAlchemy==1.4.31
  SQLAlchemy-Utils==0.38.2
  Werkzeug==1.0.1
  WTForms==2.3.3
  
  ### Describe the expected results
  
  Tell us what should happen.
  
  ```python
  flask fab create-app
  ```
  and expect to provide app name etc
  
  ### Describe the actual results
  
  Tell us what happens instead.
  
  ```pytb
  "No such command: fab"
  ```
  
  ### Steps to reproduce
  
  Do clean install on mac using pip install; activate the venv and try flask fab create-app
  
  It fails
  
  Then deactivate venv, and reactivate
  
  Now it works