pip是一個 Python 包安裝與管理工具，非常好用。
執行 pip install --upgrade pip 報錯：
DEPRECATION: Python 3.4 support has been deprecated. pip 19.1 will be the last one supporting it. Please upgrade your Python as Python 3.4 won't be maintained after March 2019 (cf PEP 429).
Requirement already up-to-date: pip in /Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/site-packages (19.1.1)
解決辦法：強制更新pip
執行：python -m pip install --upgrade pip
問題解決！