Fix HttpServer documentation

sdk/lib/io/http.dart

Index: sdk/lib/io/http.dart
diff --git a/sdk/lib/io/http.dart b/sdk/lib/io/http.dart
index 6f5eb5699c845d0caa6d062f9058d4f47a3657f1..f0c4282a228cd635f03d1ffa32a6f99872271c64 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -168,10 +168,10 @@ abstract class HttpServer implements Stream<HttpRequest> {
    *
    * By default the following headers are in this set:
    *
-   *    Content-Type: text/plain; charset=utf-8
-   *    X-Frame-Options: SAMEORIGIN
-   *    X-Content-Type-Options: nosniff
-   *    X-XSS-Protection: 1; mode=block
+   *     Content-Type: text/plain; charset=utf-8
+   *     X-Frame-Options: SAMEORIGIN
+   *     X-Content-Type-Options: nosniff
+   *     X-XSS-Protection: 1; mode=block
    *
    * If the `Server` header is added here and the `serverHeader` is set as
    * well then the value of `serverHeader` takes precedence.