Apache Airflow : airflow initdb throws ModuleNotFoundError: No module named 'werkzeug.wrappers.json'; 'werkzeug.wrappers' is not a package error : <p>On Ubuntu 18.04 with python 3.6.8, trying to install airflow. When I ran airflow initdb command, below error is thrown</p>

<pre><code>Traceback (most recent call last):
  File "/home/uEnAFpip/.virtualenvs/airflow/bin/airflow", line 21, in &lt;module&gt;
    from airflow import configuration
  File "/home/uEnAFpip/.virtualenvs/airflow/lib/python3.6/site-packages/airflow/__init__.py", line 40, in &lt;module&gt;
    from flask_admin import BaseView
  File "/home/uEnAFpip/.virtualenvs/airflow/lib/python3.6/site-packages/flask_admin/__init__.py", line 6, in &lt;module&gt;
    from .base import expose, expose_plugview, Admin, BaseView, AdminIndexView  # noqa: F401
  File "/home/uEnAFpip/.virtualenvs/airflow/lib/python3.6/site-packages/flask_admin/base.py", line 6, in &lt;module&gt;
    from flask import Blueprint, current_app, render_template, abort, g, url_for
  File "/home/uEnAFpip/.virtualenvs/airflow/lib/python3.6/site-packages/flask/__init__.py", line 20, in &lt;module&gt;
    from .app import Flask
  File "/home/uEnAFpip/.virtualenvs/airflow/lib/python3.6/site-packages/flask/app.py", line 69, in &lt;module&gt;
    from .wrappers import Request
  File "/home/uEnAFpip/.virtualenvs/airflow/lib/python3.6/site-packages/flask/wrappers.py", line 14, in &lt;module&gt;
    from werkzeug.wrappers.json import JSONMixin as _JSONMixin
ModuleNotFoundError: No module named 'werkzeug.wrappers.json'; 'werkzeug.wrappers' is not a package
</code></pre>

<p>tried pip3 install --upgrade Flask</p>
