routes: change 303 -> 301 for /static -> /assets

* should enable users' browsers to make use of the status code and cache
  the redirect (in case anybody accesses the older version of the app
  and hits /static)

app/routes.go

@@ -21,7 +21,7 @@ func (a *App) SetupRoutes() {
 	e.GET(
 		"/static/*",
 		func(c echo.Context) error {
-			return c.Redirect(http.StatusSeeOther, c.Request().URL.Path)
+			return c.Redirect(http.StatusMovedPermanently, c.Request().URL.Path)
 		},
 		middleware.Rewrite(
 			map[string]string{"/static/*": "/assets/$1"},