[Ubuntu] 安裝 labelImg

sudo pip3 install labelImg
labelImg
```
    from lxml import etree
ImportError: cannot import name 'etree'
```

解決方法
```
curl https://bootstrap.pypa.io/get-pip.py | sudo -H python3.6

sudo pip3 uninstall lxml==4.3.0
sudo pip3 install lxml==4.3.0
```

* https://blog.gtwang.org/useful-tools/labelimg-graphical-image-annotation-tool-tutorial/
* https://www.twblogs.net/a/5c6d666bbd9eee5bea9dfa09