update tutorial in line with new bitcoinjs-lib api

@locksley @sidazhang 
Yo fellas, I updated the wallet tutorial so that it works with latest BitcoinJS-lib api.

I  browserified the latest bitcoinjs-lib here: https://www.dropbox.com/s/zmqgvcz6bjpns2v/bitcoinjs-lib.min.js?dl=0

You can just upload this version on your cdn.

Also browserified helloblock in case you made changes since you uploaded the tutorial: https://www.dropbox.com/s/e2eqrl2pqaevnky/helloblock-js.min.js?dl=0