fix bug : gin config RemoveExtraSlash do not work when use static …

[mmtbak]

when i config static path in my project

code:

	app = gin.Default()
	app.RemoveExtraSlash = true
	app.Static("/static", "my-static-path")

request

# curl 127.0.0.1/static/test.json
# test.json  

# curl 127.0.0.1///static/test.json
# 404 page not found

because handler createStaticHandler.func1 ignore rPath , so change request data then handler will process request in right way .

c.Request.URL.Path = rPath

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[thinkerou]

please add some unit test, thanks!