minor #7239 Fixed tag namespace in the example of xml configuration (a-ast)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #7239).

Discussion
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Fixed tag namespace in the example of xml configuration

Closing tag <acme_hello:foo> didn't match start tag.

Commits
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dca0de5 Fixed tag namespace in the example of xml configuration

Author: xabbuh

components/dependency_injection/compilation.rst

@@ -204,7 +204,7 @@ The XML version of the config would then look like this:
         xsi:schemaLocation="http://www.example.com/symfony/schema/ http://www.example.com/symfony/schema/hello-1.0.xsd">
 
         <acme_demo:config>
-            <acme_demo:foo>fooValue</acme_hello:foo>
+            <acme_demo:foo>fooValue</acme_demo:foo>
             <acme_demo:bar>barValue</acme_demo:bar>
         </acme_demo:config>
     </container>