Bump symfony/dotenv from 4.2.1 to 4.3.4

Bumps [symfony/dotenv](https://github.com/symfony/dotenv) from 4.2.1 to 4.3.4.
- [Release notes](https://github.com/symfony/dotenv/releases)
- [Changelog](https://github.com/symfony/dotenv/blob/master/CHANGELOG.md)
- [Commits](https://github.com/symfony/dotenv/compare/v4.2.1...v4.3.4)

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

composer.json

@@ -8,7 +8,7 @@
         "josephlavin/tap": "^1.0",
         "jublonet/codebird-php": "^3.1",
         "symfony/console": "4.2.*",
-        "symfony/dotenv": "4.2.*",
+        "symfony/dotenv": "4.3.*",
         "symfony/flex": "^1.1",
         "symfony/framework-bundle": "4.2.*",
         "symfony/orm-pack": "^1.0",