python3的报错解决：
OSError: Command /home/python/.virtua...ngo3_web/bin/python3 - setuptools pkg_resources pip wheel failed with error code 2
出现上面的这个错误，依次输入以下两个命令
成功更新后，再次安装虚拟环境，便可以安装成功了
python2的报错：
OSError: Command /root/.local/share/letsencrypt/bin/python2.7 - setuptools pkg_resources pip wheel failed with error code 2 #4062
python@bogon:~$ pip -V
pip 8.1.2 from /usr/local/lib/python2.7/dist-packages (python 2.7)
python@bogon:~$ sudo pip install --upgrade pip
python@bogon:~$ mkvirtualenv datana