make reports error on master branch

```
[cauchy@kenan ~/go/src/github.com/pingcap/tipb]$ make
./generate-go.sh
generate go code...
cargo build --features gen
    Updating crates.io index
error: Package `tipb v0.0.1 (/Users/cauchy/go/src/github.com/pingcap/tipb)` does not have these features: `gen`
make: *** [rust] Error 101
```