minor symfony#11622 [Cache] Fixed typo (Nyholm)

This PR was merged into the 4.2 branch.

Discussion
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[Cache] Fixed typo

This make sure Yaml, XML and PHP configs are consistant.

Commits
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a9ac58a Fixed typo

Author: javiereguiluz

cache.rst

@@ -215,7 +215,7 @@ You can also create more customized pools:
                     # uses the "foobar.cache" pool as its backend but controls
                     # the lifetime and (like all pools) has a separate cache namespace
                     short_cache:
-                        adapter: cache.foobar
+                        adapter: foobar.cache
                         default_lifetime: 60
 
     .. code-block:: xml