Update OpenSubtitles User Agent to our own

MediaBrowser.MediaEncoding/Subtitles/OpenSubtitleDownloader.cs

@@ -46,7 +46,7 @@ namespace MediaBrowser.MediaEncoding.Subtitles
             _config.NamedConfigurationUpdating += _config_NamedConfigurationUpdating;
 
             Utilities.HttpClient = httpClient;
-            OpenSubtitles.SetUserAgent("mediabrowser.tv");
+            OpenSubtitles.SetUserAgent("jellyfin");
         }
 
         private const string PasswordHashPrefix = "h:";