v0.0.8 breaks when `go.mod` is not in repo root

The issue was introduced with #25. Cmd breaks when the go.mod is located in a subpath. Example structure:
```
project
├── .git
└── go
    ├── go.mod
    └── main.go
```

One way to solve this would be finding the go mod root. `go env GOMOD` returns the correct value or `os.DevNull` if if can't find one.