Error in request.go

I pulled the latest version of `go-gremlin/gremlin` with `go get -u github.com/go-gremlin/gremlin` and on `go run` of my application I get the following error.

```
# github.com/go-gremlin/gremlin
../../../go/pkg/mod/github.com/go-gremlin/gremlin@v0.0.0-20180314122959-0036b9fca17f/request.go:64:7: assignment mismatch: 2 variables but uuid.NewV4 returns 1 values
```