Simpler way to replace `spf13/pflag` than described in the readme

I found that I can add this to `go.mod` and that does not require me to vendor.

```
// https://github.com/cornfeedhobo/pflag
// A fork of pflag that is more maintained
replace github.com/spf13/pflag v1.0.5 => github.com/cornfeedhobo/pflag v1.1.0

exclude github.com/spf13/pflag v1.0.5
```