Update xml-crypto to 0.8.1

[Den-dp]

In our project we are not allowed to have binaries (such as *.exe and etc) in node_modules because of some security restrictions.
Unfortunately, it turned out that one of the dependencies of the samlp contains several binary files...

https://github.com/yaronn/xml-crypto/tree/master/test/validators/XmlCryptoUtilities/XmlCryptoUtilities/bin/Debug

Just recently, they released an update (0.8.1) in which those files were finally .npmignored.

Would you mind to bump xml-crypto dependency, republish samlp npm package and save the world? 😃