more easy to set value in GET method

You can also set value to GET method easily

```go
type Item struct {
        Limit int
        Skip int
        Fields string
}

item := Item {
        Limit: 3,
        Skip: 5,
        Fields: "Value",
}

res, err := goreq.Request{
        Uri: "http://localhost:3000/",
        Data: item,
}.Do()
```

The sample above will send `http://localhost:3000/?limit=3&skip=5&fields=Value`