Specify 'engines' in package.json

[kitsonk]

Type: feature

The following has been addressed in the PR:

• [X] There is a related issue
• [X] All code matches the style guide
• [ ] Unit or Functional tests are included in the PR

Description:

Adds engines property to package.json. This helps ensure the developers don't accidentally use versions of NodeJS (e.g. 4.X) that we no longer support.

Resolves #61