Upgrade gin-gonic to latest master, fix compatibility issues

vendor/github.com/gin-gonic/gin/examples/app-engine/hello.go

@@ -2,6 +2,7 @@ package hello
 
 import (
 	"net/http"
+
 	"github.com/gin-gonic/gin"
 )
 
@@ -11,13 +12,13 @@ func init() {
 	r := gin.New()
 
 	// Define your handlers
-	r.GET("/", func(c *gin.Context){
+	r.GET("/", func(c *gin.Context) {
 		c.String(200, "Hello World!")
 	})
-	r.GET("/ping", func(c *gin.Context){
+	r.GET("/ping", func(c *gin.Context) {
 		c.String(200, "pong")
 	})
 
 	// Handle all requests using net/http
 	http.Handle("/", r)
-}
+}