router.go
func (r *Router) InternalServerError(handlers ...Handler) {
	handlers = validateAndWrapHandlers(handlers)
	r.internalServerError = func(c *Context, err error) {
		c.index = 0
		c.handlers = handlers
		c.Map(err)
		c.run()
	}
}
func (r *Router) InternalServerError(handlers ...Handler) {
	handlers = validateAndWrapHandlers(handlers)
	r.internalServerError = func(c *Context, err error) {
		c.index = 0
		c.handlers = handlers
		c.Map(err)
		c.run()
	}
}
// InternalServerError configurates handler which is called when route handler returns
// error. If it is not set, default handler is used.
// Be sure to set 500 response code in your handler.