bug symfony#21276 [Cache] Fix missing use statement in FilesystemAdapter (Lctrs)

This PR was merged into the 3.2 branch.

Discussion
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[Cache] Fix missing use statement in FilesystemAdapter

| Q             | A
| ------------- | ---
| Branch?       | 3.2
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | none

Commits
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cd08f7e Add missing use statement in FilesystemAdapter

Author: nicolas-grekas

src/Symfony/Component/Cache/Adapter/FilesystemAdapter.php

@@ -11,6 +11,8 @@
 
 namespace Symfony\Component\Cache\Adapter;
 
+use Symfony\Component\Cache\Exception\CacheException;
+
 /**
  * @author Nicolas Grekas <p@tchwork.com>
  */