Check case insensitive for DDOS-GUARD (#17)

Author: mynameisbogdan

src/FlareSolverrSharp/ChallengeDetector.cs

@@ -1,4 +1,5 @@
-using System.Collections.Generic;
+using System;
+using System.Collections.Generic;
 using System.Linq;
 using System.Net;
 using System.Net.Http;
@@ -40,7 +41,7 @@ private static bool IsCloudflareProtected(HttpResponseMessage response)
                     responseHtml.Contains("<title>Access denied</title>") || // Cloudflare Blocked
                     responseHtml.Contains("<title>Attention Required! | Cloudflare</title>") || // Cloudflare Blocked
                     responseHtml.Trim().Equals("error code: 1020") || // Cloudflare Blocked
-                    responseHtml.Contains("<title>DDOS-GUARD</title>")) // DDOS-GUARD
+                    responseHtml.IndexOf("<title>DDOS-GUARD</title>", StringComparison.OrdinalIgnoreCase) > -1) // DDOS-GUARD
                     return true;
             }
 
@@ -54,4 +55,4 @@ private static bool IsCloudflareProtected(HttpResponseMessage response)
         }
 
     }
-}
+}