minor #25646 Update LICENSE year... forever (dunglas)

This PR was merged into the 2.7 branch.

Discussion
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Update LICENSE year... forever

| Q             | A
| ------------- | ---
| Branch?       | 2.7
| Bug fix?      | no
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md files -->
| Tests pass?   | yes| Fixed tickets | #... <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | n/a

By using the same trick than Facebook: https://github.com/facebook/react/blob/master/LICENSE

Commits
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8ce8bd5 Update LICENSE year... forever

Author: nicolas-grekas

LICENSE

@@ -1,4 +1,4 @@
-Copyright (c) 2004-2017 Fabien Potencier
+Copyright (c) 2004-present Fabien Potencier
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal