Signature has attribute removed

I noticed that in XMLSecurityDSig.php in some step I couldn't grasp the attribute for ds:Signature gets removed
I suspect it's in the insertSignature() function

Expected
```<ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#"></ds:Signature>```

Output
```<ds:Signature></ds:Signature>```