Check for outdated packages

This command will check the registry to see if
any (or, specific) installed packages are
currently outdated.

In the output:

• Red means there’s a newer version matching your
  semver requirements, so you should update
  now.
• Yellow indicates that there’s a newer version
  above your semver requirements (usually
  new major, or new 0.x minor) so proceed
  with caution.

npm outdated [<package-spec> ...]