Problem with relative urls when index.js is not executed from same directory

[fxedel]

Steps to reproduce

1. cd fixtures - navigate in any subfolder of the repository's root (or basically any folder except the repository's root)
2. node ../index.js - run the server from this folder
3. There's an error when visiting localhost:5000: Error: ENOENT: no such file or directory, open 'fixtures/manufacturers.json' (and probably quite a few similar errors on other pages) - the server seems to use the wrong relative urls