Fix: Add missing closing backticks to code block

Author: jnunn-aws

Libraries/src/Amazon.Lambda.AspNetCoreServer.Hosting/README.md

@@ -113,4 +113,5 @@ builder.Services.AddAWSLambdaHosting(LambdaEventSource.HttpApi, options =>
         apiResponse.Headers ??= new Dictionary<string, string>();
         apiResponse.Headers["X-Request-Id"] = context.AwsRequestId;
     };
-});
+});
+```