docs: add graceful-shutdown example for go 1.8 (#835)

* docs: add graceful-shutdown example for go 1.8

* fix testing

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

examples/graceful-shutdown/close/server.go

@@ -0,0 +1,45 @@
+// +build go1.8
+
+package main
+
+import (
+	"log"
+	"net/http"
+	"os"
+	"os/signal"
+
+	"github.com/gin-gonic/gin"
+)
+
+func main() {
+	router := gin.Default()
+	router.GET("/", func(c *gin.Context) {
+		c.String(http.StatusOK, "Welcome Gin Server")
+	})
+
+	server := &http.Server{
+		Addr:    ":8080",
+		Handler: router,
+	}
+
+	quit := make(chan os.Signal)
+	signal.Notify(quit, os.Interrupt)
+
+	go func() {
+		<-quit
+		log.Println("receive interrupt signal")
+		if err := server.Close(); err != nil {
+			log.Fatal("Server Close:", err)
+		}
+	}()
+
+	if err := server.ListenAndServe(); err != nil {
+		if err == http.ErrServerClosed {
+			log.Println("Server closed under request")
+		} else {
+			log.Fatal("Server closed unexpect")
+		}
+	}
+
+	log.Println("Server exist")
+}