fixed bug. Multi routine call WriteMessage will make race for same bu…

[lpflpf]

// issue.go
package main

import (
    "time"
    "gopkg.in/Graylog2/go-gelf.v2/gelf"
)

func main() {
    addr := ""
	writer, _ := gelf.NewTCPWriter(addr)
	parall := 10000
	goroutineSize := 100
	for q := 0; q < goroutineSize; q++ {
		go func() {
			for j := 0; j < parall/goroutineSize; j++ {
				writer.WriteMessage(&gelf.Message{
					Version:  "1.0",
					Host:     "hostname",
					Short:    "-",
					TimeUnix: float64(time.Now().UnixNano()),
					Level:    6,
					Facility: "",
				})
			}
		}()
	}
	select {}
}

run go run -race issue.go; will get DATA RACE WARNING.
it is a bugfix: https://github.com/lpflpf/go-gelf/tree/v2

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[dennisoelkers]

Hey @lpflpf, thanks for your submission. What is the reason you closed this PR?

[lpflpf]

It has a mistake in submission. It have been submited again.

#31