DATA RACE in resty.(*Client).execute()

Hello, 
I am use resty in multi-goroutine and case the DATA RACE

test.go
`package main

import (
    "github.com/go-resty/resty"
    "sync"
)

func main() {
    w := sync.WaitGroup{}
    for i := 0; i < 50; i++ {
        w.Add(1)
        go func() {
            defer w.Done()
            resty.R().Get("http://httpbin.org/get")
        }()
    }
    w.Wait()
}`
`go run -race test.go`
