escaped backslash not converted to real backslash

```sh
$ cat /tmp/test.env 
TEST="namespace\\class"

$ source /tmp/test.env && echo $TEST
namespace\class  

$ php -r 'require_once "vendor/autoload.php"; echo  M1\Env\Parser::parse(file_get_contents("/tmp/test.env"))["TEST"].PHP_EOL;'
namespace\\class
```
expected: `namespace\class`