centos-rockmongo - install of mongo.so broken due missing make

Hello!
  Tried example from http://openshift.github.io/geard/deploy_with_geard.html but instead of admin page got response "To make things right, you must install php_mongo module. Here for installation documents on PHP.net."

This error is caused by install error of mongo.so due missing make.

Proposed fix: add "yum install -y make" to Dockerfile
