如何为Golang Gin框架返回gzip响应

I'm trying to return a gzip response using the golang framework gin.

package main

import (
    "fmt"
    "github.com/gin-gonic/contrib/gzip"
    "github.com/gin-gonic/gin"
    "time"
)

func main() {
    r := gin.Default()
    r.Use(gzip.Gzip(gzip.DefaultCompression))
    r.GET("/ping", func(c *gin.Context) {
        c.String(200, "pong "+fmt.Sprint(time.Now().Unix()))
    })

    // Listen and Server in 0.0.0.0:8080
    r.Run(":8080")
}

When I use this example its not returning gzipped content.

With the code above I get the following output from curl

curl -v -H "Accept-Encoding: gzip" 'http://localhost:8080/ping'

Trying ::1...
Connected to localhost (::1) port 8080 (#0) GET /ping HTTP/1.1 Host: localhost:8080 User-Agent: curl/7.43.0 Accept: / Accept-Encoding: gzip
< HTTP/1.1 200 OK
< Content-Encoding: gzip
< Content-Type: text/plain; charset=utf-8
< Vary: Accept-Encoding
< Date: Mon, 18 Jul 2016 17:20:56 GMT
< Content-Length: 38
<

Connection #0 to host localhost left intact pong 1468862456?n????

Notice the content is not gzipped and there are extra junk characters added on.

"?n????"

So far I can't figure out how to get it to return gzip. I think there is a mistake in the example code but I'm having trouble figuring it out.

Thank you in advance.