Fix the yml parser issue with unescaped backslash in double quoted st…

…ring

https://github.com/symfony/yaml/blob/master/CHANGELOG.md#300

tests/Doctrine/DBAL/Migrations/Tests/Configuration/_files/config_migrations_list.yml

@@ -2,6 +2,6 @@
 name: Doctrine Sandbox Migrations
 table_name: doctrine_migration_versions_test
 migrations:
-  - { "class": "Doctrine\DBAL\Migrations\Tests\Stub\Version1Test", "version": "Version1Test" }
-  - { "class": "Doctrine\DBAL\Migrations\Tests\Stub\Version2Test", "version": "Version2Test" }
-  - { "class": "Doctrine\DBAL\Migrations\Tests\Stub\Version3Test", "version": "Version3Test" }
+  - { 'class': 'Doctrine\DBAL\Migrations\Tests\Stub\Version1Test', 'version': 'Version1Test' }
+  - { 'class': 'Doctrine\DBAL\Migrations\Tests\Stub\Version2Test', 'version': 'Version2Test' }
+  - { 'class': 'Doctrine\DBAL\Migrations\Tests\Stub\Version3Test', 'version': 'Version3Test' }