Support .env.test when process.env.NODE_ENV === 'test'

[antonakospanos]

Sourcing .env so that we can easily override the default configs during the local development is a great feature but it's also very common to need an override during test execution.

Sourcing .env.test in that case is sth supported in similar libraries for other frameworks too (i.e. RoR)

[nikostoulas]

@antonakospanos if the env does not contain secrets then you could utilize: https://github.com/Workable/job-board/blob/master/src/config/env/test.json