Do not use `$(pwd)` in `Makefile.production` as it is error-prone

[simon-wacker]

For details and an alternative see https://stackoverflow.com/questions/18136918/how-to-get-current-relative-directory-of-your-makefile/18137056#18137056

We currently use it in 756e588#diff-acb6b529d5fc00dd2cba18d12537de28eec02a895d8f6c88ea87e2b7690a3b01R230 and 756e588#diff-acb6b529d5fc00dd2cba18d12537de28eec02a895d8f6c88ea87e2b7690a3b01R235

Related to building-envelope-data/metabase#133