#16 add Content-Type

Author: phnx47

src/Prometheus.Client.AspNetCore/PrometheusExtensions.cs

@@ -42,6 +42,7 @@ public static IApplicationBuilder UsePrometheusServer(this IApplicationBuilder a
                 coreapp.Run(async context =>
                 {
                     var response = context.Response;
+                    response.ContentType = "text/plain; version=0.0.4";
 
                     using (var outputStream = response.Body)
                     {
@@ -70,4 +71,4 @@ private static void RegisterCollectors(PrometheusOptions options)
             options.CollectorRegistryInstance.RegisterOnDemandCollectors(options.Collectors);
         }
     }
-}
+}