Bump symfony/stopwatch from 5.1.7 to 5.1.8

Bumps [symfony/stopwatch](https://github.com/symfony/stopwatch) from 5.1.7 to 5.1.8.
- [Release notes](https://github.com/symfony/stopwatch/releases)
- [Changelog](https://github.com/symfony/stopwatch/blob/5.x/CHANGELOG.md)
- [Commits](https://github.com/symfony/stopwatch/compare/v5.1.7...v5.1.8)

Signed-off-by: dependabot[bot] <support@github.com>

composer.json

@@ -49,7 +49,7 @@
         ]
     },
     "require-dev" : {
-        "symfony/stopwatch" : "5.1.7",
+        "symfony/stopwatch" : "5.1.8",
         "phpunit/phpunit" : "^7",
         "roave/security-advisories": "dev-master"
     }