minor symfony#12801 Use HttpKernel Component (demyanovs)

This PR was submitted for the master branch but it was merged into the 3.4 branch instead (closes symfony#12801). Discussion ---------- Use HttpKernel Component We need to import Symfony\Component\HttpKernel before using it. <!-- If your pull request fixes a BUG, use the oldest maintained branch that contains the bug (see https://symfony.com/roadmap for the list of maintained branches). If your pull request documents a NEW FEATURE, use the same Symfony branch where the feature was introduced (and `master` for features of unreleased versions). --> Commits ------- 2cf09a9 Use HttpKernel Component

Author: javiereguiluz

create_framework/http_kernel_httpkernelinterface.rst

@@ -56,6 +56,7 @@ PHP; it implements ``HttpKernelInterface`` and wraps another
  // example.com/web/front.php
 
  // ...
+ use Symfony\Component\HttpKernel;
 
  $framework = new Simplex\Framework($dispatcher, $matcher, $controllerResolver, $argumentResolver);
  $framework = new HttpKernel\HttpCache\HttpCache(