add country header to app client

this header is now required in the acquireVehicles API call
otherwise the API returns the error "Refresh Token has expired"

Author: zivillian

libgwmapi.test/GwmApiClientTest.cs

@@ -239,6 +239,7 @@ private GwmApiClient GetAuthenticatedClient()
     {
         var client = GetClient();
         client.SetAccessToken("<accessToken>");
+        client.Country = "<country>";
         return client;
     }
 }

libgwmapi/GwmApiClient.cs

@@ -50,6 +50,8 @@ public string Country
         {
             _h5Client.DefaultRequestHeaders.Remove("country");
             _h5Client.DefaultRequestHeaders.Add("country", value);
+            _appClient.DefaultRequestHeaders.Remove("country");
+            _appClient.DefaultRequestHeaders.Add("country", value);
         }
     }