Fix typo in method setETag. Correct method name is setEtag

Artem Henvald · Artem Henvald · commit 6a2a8770fa3d · 2018-04-04T15:16:12.000+03:00
diff --git a/http_cache/validation.rst b/http_cache/validation.rst
@@ -200,7 +200,7 @@ exposing a simple and efficient pattern::
 
             // create a Response with an ETag and/or a Last-Modified header
             $response = new Response();
-            $response->setETag($article->computeETag());
+            $response->setEtag($article->computeETag());
             $response->setLastModified($article->getPublishedAt());
 
             // Set response as public. Otherwise it will be private by default.
