minor #287 Wrong class used in turbo streams (htmlshaman1, weaverryan)

This PR was merged into the 2.x branch.

Discussion
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Wrong class used in turbo streams

TurboBundle::STREAM_FORMAT doesn't exist, that static variable was moved to TurboStreamResponse::STREAM_FORMAT.
Also the stream didn't work for me unless I changed:
$this->render('task/success.stream.html.twig', ['task' => $task]); to $this->render('task/success.stream.html.twig', ['task' => $task], new TurboStreamResponse());

| Q             | A
| ------------- | ---
| Bug fix?      | yes/no
| New feature?  | yes/no <!-- please update src/**/CHANGELOG.md files -->
| Tickets       | Fix #... <!-- prefix each issue number with "Fix #", no need to create an issue if none exist, explain below instead -->
| License       | MIT

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Commits
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1abee43 minor cleanups
320efe3 I think I got it
5eef995 Added a message about it was done in version 2.0
e411a77 Wrong class used in turbo streams

Author: weaverryan

src/Turbo/Resources/doc/index.rst

@@ -300,6 +300,11 @@ clients. There are two main ways to receive the updates:
 Forms
 ^^^^^
 
+.. versionadded:: 2.1
+  
+    Prior to 2.1, ``TurboStreamResponse::STREAM_FORMAT`` was used instead of ``TurboBundle::STREAM_FORMAT``.
+    Also, one had to return a new ``TurboStreamResponse()`` object as the third argument to ``$this->render()``.
+
 Let's discover how to use Turbo Streams to enhance your `Symfony forms`_::
 
     // src/Controller/TaskController.php