When using Ember CLI http-mock is it possible to stop express updating?

I have been using http-mock with Ember CLI. Today I generated a new http-mock with

ember generate http-mock myobject

I found afterwards that my package.json file had been updated from express 4.12.4 to 4.13.0

 - "express": "^4.12.4",

 + "express": "^4.13.0",

Our Ember CLI version has remained constant, it just so happens express released a new version (http://ift.tt/1IAdeXq) between the first time we used http-mock and today.

We would rather manage dependency changes by themselves as and when we want to, but still be able to create new http-mock's when we want them. Can I run the command slightly differently to prevent express upgrading it's version?