Use URL_BASE in index mapper

src/NzbDrone.Api/Frontend/Mappers/IndexHtmlMapper.cs

@@ -94,7 +94,7 @@ namespace NzbDrone.Api.Frontend.Mappers
             text = text.Replace("APP_VERSION", BuildInfo.Version.ToString());
             text = text.Replace("APP_BRANCH", _configFileProvider.Branch.ToLower());
             text = text.Replace("APP_ANALYTICS", _analyticsService.IsEnabled.ToString().ToLowerInvariant());
-            text = text.Replace("URL_BASE", _configFileProvider.UrlBase);
+            text = text.Replace("URL_BASE", URL_BASE);
 
             _generatedContent = text;