CVE-2019-11325: Fix escaping of strings in VarExporter

Affected versions Symfony 4.2.0 to 4.2.11 and 4.3.0 to 4.3.7 versions of the Symfony VarExporter component are affected by this security issue. The issue has been fixed in Symfony 4.2.12 and 4.3.8. Description Some strings were not properly escaped when being dumped by the VarExporter component...