Accept HttpStatusCode.OK in response to newOrder request

That's the way Digicert does it, and not forbidden by the RFC

src/ACMESharp/Protocol/AcmeProtocolClient.cs

@@ -376,7 +376,7 @@ public async Task<OrderDetails> CreateOrderAsync(IEnumerable<string> dnsIdentifi
                     new Uri(_http.BaseAddress, Directory.NewOrder),
                     method: HttpMethod.Post,
                     message: message,
-                    expectedStatuses: new[] { HttpStatusCode.Created },
+                    expectedStatuses: new[] { HttpStatusCode.Created, HttpStatusCode.OK },
                     cancel: cancel);
 
             var order = await DecodeOrderResponseAsync(resp);