Update ApiNgJsonRpcOperations.java

Hi, I have been using this code for one week now and I just realised I was not receiving the stakes in the right currency because of the currencyCode was not passed to request. I am not sure, if it was omitted on purpose or not but I wanted to let you know..                 Thanks in advance, Alain
Merge pull request #10 from aquenneville/patch-1

Update ApiNgJsonRpcOperations.java to include currencyCode, thanks @aquenneville.