minor symfony#25421 grammar typo in docs (michaelKaefer)

This PR was merged into the 4.1-dev branch.

Discussion
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grammar typo in docs

| Q             | A
| ------------- | ---
| Branch?       | master for features / 2.7 up to 4.0 for bug fixes <!-- see below -->
| Bug fix?      | yes/no
| New feature?  | yes/no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | yes/no
| Deprecations? | yes/no <!-- don't forget to update UPGRADE-*.md files -->
| Tests pass?   | yes/no
| Fixed tickets | #... <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | symfony/symfony-docs#... <!--highly recommended for new features-->

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Commits
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d53c889 grammar typo in docs

Author: chalasr

src/Symfony/Component/Lock/StoreInterface.php

@@ -31,7 +31,7 @@ interface StoreInterface
     public function save(Key $key);
 
     /**
-     * Waits a key becomes free, then stores the resource.
+     * Waits until a key becomes free, then stores the resource.
      *
      * If the store does not support this feature it should throw a NotSupportedException.
      *