add npmDependency specification

Signed-off-by: Jason Van Pelt <jvanpelt@newrelic.com>
fail on package.json parse error and missing file

Signed-off-by: Jason Van Pelt <jvanpelt@newrelic.com>
Merge pull request #6 from jasonpvp/jasonpvp/add_npm_dependencies

add npmDependency and npmDevDependency specifications