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**Apache Airflow version**: 2.0.0b1


**Kubernetes version (if you are using kubernetes)** (use `kubectl version`): NA

**Environment**:

- **Cloud provider or hardware configuration**:
- **OS** (e.g. from /etc/os-release): macOS
- **Kernel** (e.g. `uname -a`):
- **Install tools**:
- **Others**:

**What happened**:
Installed apache-airlfow==2.0.0b1 using pip. 
Running `airflow webserver` gave the following error:
```
Traceback (most recent call last):
  File "/Users/abagri/Workspace/service-workflows/venv/bin/airflow", line 8, in <module>
    sys.exit(main())
  File "/Users/abagri/Workspace/service-workflows/venv/lib/python3.8/site-packages/airflow/__main__.py", line 40, in main
    args.func(args)
  File "/Users/abagri/Workspace/service-workflows/venv/lib/python3.8/site-packages/airflow/cli/cli_parser.py", line 49, in command
    func = import_string(import_path)
  File "/Users/abagri/Workspace/service-workflows/venv/lib/python3.8/site-packages/airflow/utils/module_loading.py", line 32, in import_string
    module = import_module(module_path)
  File "/usr/local/Cellar/python@3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 975, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 671, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 783, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/Users/abagri/Workspace/service-workflows/venv/lib/python3.8/site-packages/airflow/cli/commands/webserver_command.py", line 43, in <module>
    from airflow.www.app import cached_app, create_app
  File "/Users/abagri/Workspace/service-workflows/venv/lib/python3.8/site-packages/airflow/www/app.py", line 39, in <module>
    from airflow.www.extensions.init_views import (
  File "/Users/abagri/Workspace/service-workflows/venv/lib/python3.8/site-packages/airflow/www/extensions/init_views.py", line 25, in <module>
    from airflow.api_connexion.exceptions import common_error_handler
ModuleNotFoundError: No module named 'airflow.api_connexion.exceptions'
```
<!-- (please include exact error messages if you can) -->

**What you expected to happen**:
Expect this command to start the webserver
<!-- What do you think went wrong? -->

**How to reproduce it**:
Install a fresh version of airflow, run `airflow db init` followed by `airflow webserver`
<!---

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If you are using kubernetes, please attempt to recreate the issue using minikube or kind.

## Install minikube/kind

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- Kind https://kind.sigs.k8s.io/docs/user/quick-start/

If this is a UI bug, please provide a screenshot of the bug or a link to a youtube video of the bug in action

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--->


**Anything else we need to know**:

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docs/conf.py
# 
    'theme_analytics_id': 'UA-140539454-1',
}
if airflow_theme_is_available:
    html_context = {
        # 
        #
        # 
        #
        # 
        # 
        # 
        #
        # 
        # 
        # 
        # 
        #
        'theme_vcs_pageview_mode': 'edit',
        'conf_py_path': '/docs/',
        'github_user': 'apache',
        'github_repo': 'airflow',
        'github_version': 'master',
        'display_github': 'master',
        'suffix': '.rst',
    }
# 
# -- Options for sphinxcontrib.jinjac ------------------------------------------
# 
# Jinja context