解决dockerfile创建镜像时pip install报错的bug

项目场景：

使用docker-compose创建django容器

问题描述

 > [5/5] RUN /bin/bash -c 'source ~/.bashrc && python3 -m pip install -r requirements.txt -i https://pypi.tuna.tsinghua.edu.cn/simple':              
0.954 Looking in indexes: https://pypi.tuna.tsinghua.edu.cn/simple                                                                                   
15.98 WARNING: Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7fefee58f1d0>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/aliyun-python-sdk-core/                                                                                                                        
31.50 WARNING: Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7fefea3e8d10>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/aliyun-python-sdk-core/
47.53 WARNING: Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7fefea3e9710>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/aliyun-python-sdk-core/
64.55 WARNING: Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7fefea3e9f50>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/aliyun-python-sdk-core/
83.57 WARNING: Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.HTTPSConnection object at 0x7fefea3ea8d0>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/aliyun-python-sdk-core/
98.59 ERROR: Could not find a version that satisfies the requirement aliyun-python-sdk-core (from versions: none)
98.59 ERROR: No matching distribution found for aliyun-python-sdk-core
113.6 WARNING: There was an error checking the latest version of pip.