[Security] Bump symfony/symfony from 3.1.10 to 3.4.35

Bumps [symfony/symfony](https://github.com/symfony/symfony) from 3.1.10 to 3.4.35. **This update includes security fixes.**
- [Release notes](https://github.com/symfony/symfony/releases)
- [Changelog](https://github.com/symfony/symfony/blob/v3.4.35/CHANGELOG-3.4.md)
- [Commits](symfony/symfony@v3.1.10...v3.4.35)

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

composer.json

@@ -21,7 +21,7 @@
         "ext-mbstring": "*",
         "ext-curl": "*",
         "ext-xml": "*",
-        "symfony/symfony": "3.2.*",
+        "symfony/symfony": "3.4.*",
         "doctrine/orm": "^2.5",
         "doctrine/doctrine-bundle": "^1.6",
         "doctrine/doctrine-cache-bundle": "^1.2",