Removed nameof for ArgumentNullException that is specific to C# 6.0

Owin.Security.Providers/Shopify/ShopifyAuthenticationExtensions.cs

@@ -14,12 +14,12 @@
         {
             if (null == app)
             {
-                throw new ArgumentNullException(nameof(app));
+                throw new ArgumentNullException("app");
             }
 
             if (null == options)
             {
-                throw new ArgumentNullException(nameof(options));
+                throw new ArgumentNullException("options");
             }
 
             app.Use(typeof(ShopifyAuthenticationMiddleware), app, options);