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**Apache Airflow version**:

1.10.12

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

N/A

**Environment**:

- **Cloud provider or hardware configuration**: 
- **OS** (e.g. from /etc/os-release): Centos 7
- **Kernel** (e.g. `uname -a`): 3.10.0-229.el7.x86_64
- **Install tools**: pip 9.0.3 from /usr/lib/python3.6/site-packages (python 3.6)
- **Others**:

**What happened**:

Following the instructions [here](http://airflow.apache.org/docs/stable/start.html), I encountered an issue at the `airflow initdb` stage:

```
[xxx@xxx ~]# airflow initdb
Traceback (most recent call last):
  File "/usr/local/bin/airflow", line 26, in <module>
    from airflow.bin.cli import CLIFactory
  File "/usr/local/lib/python3.6/site-packages/airflow/bin/cli.py", line 94, in <module>
    api_module = import_module(conf.get('cli', 'api_client'))  # type: Any
  File "/usr/lib64/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "/usr/local/lib/python3.6/site-packages/airflow/api/client/local_client.py", line 24, in <module>
    from airflow.api.common.experimental import delete_dag
  File "/usr/local/lib/python3.6/site-packages/airflow/api/common/experimental/delete_dag.py", line 26, in <module>
    from airflow.models.serialized_dag import SerializedDagModel
  File "/usr/local/lib/python3.6/site-packages/airflow/models/serialized_dag.py", line 35, in <module>
    from airflow.serialization.serialized_objects import SerializedDAG
  File "/usr/local/lib/python3.6/site-packages/airflow/serialization/serialized_objects.py", line 28, in <module>
    import cattr
  File "/usr/local/lib/python3.6/site-packages/cattr/__init__.py", line 1, in <module>
    from .converters import Converter, GenConverter, UnstructureStrategy
  File "/usr/local/lib/python3.6/site-packages/cattr/converters.py", line 16, in <module>
    from attr import fields, resolve_types
ImportError: cannot import name 'resolve_types'
```

<!-- (please include exact error messages if you can) -->

**What you expected to happen**:

I expected the Airflow DB to be initialised as per the instructions. 

<!-- What do you think went wrong? -->

**How to reproduce it**:
<!---

As minimally and precisely as possible. Keep in mind we do not have access to your cluster or dags.

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

## Install minikube/kind

- Minikube https://minikube.sigs.k8s.io/docs/start/
- 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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To record a screencast, mac users can use QuickTime and then create an unlisted youtube video with the resulting .mov file.

--->

On a fresh installation, follow the Quick Start guide until the `apache initdb` stage.

**Anything else we need to know**:

Investigation suggests that this was caused by a Python dependency; specifically `cattrs==1.1.0`, which was released yesterday (2020-10-29). Downgrading `cattrs` manually to 1.0.0 does fix the issue and allows the Airflow database to be initialised:

```
[xxx@xxx ~]# pip3 install cattrs==1.0.0
Collecting cattrs==1.0.0
  Downloading https://files.pythonhosted.org/packages/17/5b/6afbdaeb066ecf8ca28d85851048103ac80bb169491a54a14bd39823c422/cattrs-1.0.0-py2.py3-none-any.whl
Requirement already satisfied: attrs>=17.3 in /usr/local/lib/python3.6/site-packages (from cattrs==1.0.0)
Installing collected packages: cattrs
  Found existing installation: cattrs 1.1.0
    Uninstalling cattrs-1.1.0:
      Successfully uninstalled cattrs-1.1.0
Successfully installed cattrs-1.0.0
[xxx@xxx ~]# airflow initdb            
DB: sqlite:////path/to/airflow.db
[2020-10-30 09:36:05,431] {db.py:378} INFO - Creating tables
INFO  [alembic.runtime.migration] Context impl SQLiteImpl.
INFO  [alembic.runtime.migration] Will assume non-transactional DDL.
INFO  [alembic.runtime.migration] Running upgrade  -> e3a246e0dc1, current schema
INFO  [alembic.runtime.migration] Running upgrade e3a246e0dc1 -> 1507a7289a2f, create is_encrypted
/usr/local/lib/python3.6/site-packages/alembic/ddl/sqlite.py:44: UserWarning: Skipping unsupported ALTER for creation of implicit constraintPlease refer to the batch mode feature which allows for SQLite migrations using a copy-and-move strategy.
...
Done.
```

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setup.py
]
jenkins = [
    'python-jenkins>=1.0.0',
]
jira = [
    'JIRA>1.0.7',
]
kerberos = [
    'pykerberos>=1.1.13',
    'requests_kerberos>=0.10.0',
    'thrift_sasl>=0.2.0',
]
kubernetes = [
    'cryptography>=2.0.0',
    'kubernetes>=3.0.0',
]
kylin = [
    'kylinpy>=2.6'
]
ldap = [
    'ldap3>=2.5.1',
]
mongo = [
    'dnspython>=1.13.0,<2.0.0',
    'pymongo>=3.6.0',
]
mssql = [
    'pymssql~=2.1,>=2.1.5',
]
mysql = [