remove new lines from signature

certain frameworks will generate signatures with `\n`. If these are not removed, the signature verification fails.

```xml
   <ds:SignatureValue>
        QCZDkL1tsg1HH3mAWwP2saiQTSeu0lM7fusBBil/tCtjdSleex+kRDLZocjuK+Up1/7JhKCNUQ6H
        NqWtqfGURiqJZ+29QZ1w6bmOwausg1bRBFoEmRGtpDxu0p4sWziNw2tyO5oVVH60hAffYGN70yH4
        E1wkuzeaEXNXXFhAJxsNTj5JGDfcewU9R4/UmrNUXY7kvBQWpQrb5TNS63k/HahGl7zO72ekQU+N
        SATSA2ohISOhmPSmErAUZBB6gARCk+OlVFWtU/MRqE2Z9QaW6wdbPgVH4wbXnp8bG1u44Ty9mACX
        b+8WOAw4pXNLWc5Y+gJiQriGrozzoJPh5F/qCg==
    </ds:SignatureValue>
```