终端下运行：sudo pip install xgboost
有时不是sudo用户，提示错误，并且卡住不运行。
The directory '/home/jiyuan/.cache/pip/http' or its parent directory is not owned by the current user and the cache has been disabled. Please check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
The directory '/home/jiyuan/.cache/pip' or its parent directory is not owned by the current user and caching wheels has been disabled. check the permissions and owner of that directory. If executing pip with sudo, you may want sudo's -H flag.
直接用：pip install xgboost 可以成功，（也不知道为什么？）
更新安装包：以pip为例，pip install --upgrade pip
就算原来没有的包，也可以pip install --upgrade gensim