npm shrinkwrap is useful, but maddening (once it's in place and you want to update a package).
Say you've got a package.json with module ember-cli as a devDependency currently at version 1.13.1. And you have an npm-shrinkwrap.json file too, generated with the --dev flag.
If you change the version of ember-cli to, say, 1.13.8 in package.json and run npm install, nothing will happen.
If you do that and manually change references in the shrinkwrap file, you will still have trouble (as nested dependencies may now be incorrect).
