Update "/token-request-url" to include the "dk" parameter.

[craigfrancis]

Not sure if this should be in the SDK or here...

When calling "/token-request-url", the returned URL needs to be edited to include the dk parameter.

As in, I need to append “&dk=4qY7lqQw8NOl9gng0ZHgT4xdiDqxqoGVutuZwrUYQsI” to the end of that URL... well, at least on the Live server, it's fine when working with the SANDBOX.

I assume the generateTokenRequestUrl() method needs to be updated:

https://github.com/tokenio/merchant-proxy/blob/master/src/main/java/server/ProxyServer.java#L188