minor symfony#10078 Fixing syntax error (weaverryan)

This PR was merged into the 3.4 branch.

Discussion
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Fixing syntax error

Reported on Slack by magnus!

Commits
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3107226 Fixing syntax error

Author: javiereguiluz

components/asset.rst

@@ -161,7 +161,7 @@ In those cases, use the
     use Symfony\Component\Asset\Package;
     use Symfony\Component\Asset\VersionStrategy\JsonManifestVersionStrategy;
 
-    $package = new Package(new JsonManifestVersionStrategy(__DIR__'./rev-manifest.json'));
+    $package = new Package(new JsonManifestVersionStrategy(__DIR__.'/rev-manifest.json'));
 
     echo $package->getUrl('css/app.css');
     // result: build/css/app.b916426ea1d10021f3f17ce8031f93c2.css