minor symfony#23797 Don't force lowercase for hasher values (javiereguiluz)

This PR was merged into the 4.0-dev branch.

Discussion
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Don't force lowercase for hasher values

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

In Symfony 4.x we no longer modify the service ids to lowercase them, so this PR tweaks the hasher introduced in symfony#23766.

Commits
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156cb70 [DI] Don't force lowercase for hasher values

Author: nicolas-grekas

src/Symfony/Component/DependencyInjection/ContainerBuilder.php

@@ -1328,7 +1328,7 @@ public static function hash($value)
     {
         $hash = substr(base64_encode(hash('sha256', serialize($value), true)), 0, 7);
 
-        return str_replace(array('/', '+'), array('.', '_'), strtolower($hash));
+        return str_replace(array('/', '+'), array('.', '_'), $hash);
     }
 
     /**