Fails to run with `go 1.N.P` go.mod syntax

Our `go-licenses save` run fails with the 1.N.P Go version go.mod syntax with lots of:

```
E0422 10:52:12.907282  169280 library.go:159] Package flag does not have module info. Non go modules projects are no longer supported. For feedback, refer to https://github.com/google/go-licenses/issues/128.
...
```

and no output produced.