更新tensorflow时遇到报错
Found existing installation: enum34 1.0.4
Cannot uninstall 'enum34'. It is a distutils installed project and thus we cannot accurately determine which files belong to it which would lead to only a partial uninstall.
解决方法如下：
pip install enum34 --upgrade --ignore-installed
成功升级enum34模块到最新版本，然后顺利升级TensorFlow：
pip install tensorflow --upgrade