在ubuntu 18.04中，使用php 5.6，php5.6-fpm，nginx，使用ubuntu的mongodb
composer require mongodb/mongodb
错误
Using version ^1.4 for mongodb/mongodb
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.
Problem 1
- mongodb/mongodb 1.4.2 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb has the wrong version (1.4.2) installed.
- mongodb/mongodb 1.4.1 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb has the wrong version (1.4.2) installed.
- mongodb/mongodb 1.4.0 requires ext-mongodb ^1.5.0 -> the requested PHP extension mongodb has the wrong version (1.4.2) installed.
- Installation request for mongodb/mongodb ^1.4 -> satisfiable by mongodb/mongodb[1.4.0, 1.4.1, 1.4.2].
有同样的问题，我可以用它来解决它：
composer require "mongodb/mongodb=^1.4.2" --ignore-platform-reqs