* composer 安装 mongodb 时候出现版本提示：
```
Your requirements could not be resolved to an installable set of packages.
Problem 1
- mongodb/mongodb 1.4.1 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb has the wrong version (1.1.5) installed.
- mongodb/mongodb 1.4.0 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb has the wrong version (1.1.5) installed.
- mongodb/mongodb 1.3.2 requires ext-mongodb ^1.4.0 -> the requested PHP extension mongodb has the wrong version (1.1.5) installed.
- mongodb/mongodb 1.3.1 requires ext-mongodb ^1.4.0 -> the requested PHP extension mongodb has the wrong version (1.1.5) installed.
- mongodb/mongodb 1.3.0 requires ext-mongodb ^1.4.0 -> the requested PHP extension mongodb has the wrong version (1.1.5) installed.
- Installation request for mongodb/mongodb ^1.3 -> satisfiable by mongodb/mongodb[1.3.0, 1.3.1, 1.3.2, 1.4.0, 1.4.1].
查看 php 的mongodb 扩展： echo phpinfo();
更新扩展sudo apt-get install software-properties-common
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
apt-get install php7.0-mongodb
重启启动 apache
` sudo systemctl restart apache2.service `
重启后刷新 phpinfo 才看到 mongodb 的版本变化。