Implement a test using only production dependencies

[mnkhouri]

Some modules, such as Typescript, are optional at runtime. There should be a test that verifies that the program operates correctly when these optional dependencies are not present. #280 is an example of a bug that would be nice to catch in tests.

For example in travis.yml, there could be:

script:
  - npm prune --production && npm run depcheck

^^ This isn't the best solution because it modifies the Travis working directory. Ideally, that test would run in its own container, but the current travis.yml isn't set up that way (yet).

[mnkhouri]

As stated in #282 (comment):

This one is hard. If the environment is complicated and stability is low, it may be not worth.

I agree it's probably not worth it. Unless someone has a neat idea for this, I'll close the issue in a week or two