`SSL_CERT_FILE` has been replaced with `NIX_SSL_CERT_FILE`.
Before this change using `fetchdarcs` resulted in an error message like:
```
Identifying repository http://hub.darcs.net/scravy/easyplot inventory
darcs failed: Not a repository: http://hub.darcs.net/scravy/easyplot (Peer certificate cannot be authenticated with given CA certificates)
HINT: Do you have the right URI for the repository?
builder for ‘/nix/store/imyvcs6lvb5yva66krc5wk39931sam8v-fetchdarcs.drv’ failed with exit code 2
```
a81f45386b