**Apache Airflow version**: 2.0.0

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

**Environment**: 
* local Ubuntu 18.04 LTS / 
* docker-compose version 1.25.3, build d4d1b42b
* docker  20.10.1, build 831ebea

**What happened**:

when enabling xcom push for a docker operator the following error is thrown after the task finishes succesfully:
`TypeError: Object of type bytes is not JSON serializable`


**What you expected to happen**:

* error is not thrown
* if xcom_all is True: xcom contains all log lines
* if xcom_all is False: xcom contains last log line


**How to reproduce it**:

see docker compose and readme here:
https://github.com/AlessioM/airflow-xcom-issue

airflow/providers/docker/operators/docker.py
#
#
#
"""Implements Docker operator"""
import ast
from tempfile import TemporaryDirectory
from typing import Dict, Iterable, List, Optional, Union
from docker import APIClient, tls
from docker.errors import APIError
from docker.types import Mount
from airflow.exceptions import AirflowException
from airflow.models import BaseOperator
from airflow.providers.docker.hooks.docker import DockerHook
class DockerOperator(BaseOperator):