Update examples with the latest version of bitcore v0.13.x

[TOMOAKI12345]

examples/01.createChannel.js
fs.writeFileSync('unsigned.refund.log', consumer.setupRefund().toJSON());
write [object Object]

so that is not working
examples/02.signRefund.js
var refund = JSON.parse(String(fs.readFileSync('unsigned.refund.log')));

[braydonf]

The behavior or toJSON() has recently changed in the latest Bitcore release (see release notes), and JSON.stringify will return a string:

JSON.stringify(consumer.setupRefund())

The examples need to be updated.

[braydonf]

Updated in: #37