Bump default API version for VK (#590)

Updates default API version to 5.131.

Author: leotsarev

src/AspNet.Security.OAuth.Vkontakte/VkontakteAuthenticationDefaults.cs

@@ -52,6 +52,6 @@ public static class VkontakteAuthenticationDefaults
         /// <summary>
         /// Default API version.
         /// </summary>
-        public const string ApiVersion = "5.78";
+        public const string ApiVersion = "5.131";
     }
 }

test/AspNet.Security.OAuth.Providers.Tests/Vkontakte/bundle.json

@@ -13,7 +13,7 @@
       }
     },
     {
-      "uri": "https://api.vk.com/method/users.get.json?access_token=secret-access-token&v=5.78&fields=id,first_name,last_name,photo_rec,photo,hash",
+      "uri": "https://api.vk.com/method/users.get.json?access_token=secret-access-token&v=5.131&fields=id,first_name,last_name,photo_rec,photo,hash",
       "contentFormat": "json",
       "contentJson": {
         "response": [