doc: default minconf for getbalance should be 0
doc: default minconf for getbalance should be 0

Former-commit-id: b90ebb37217832769ab99b0c35a963eaa4f50777
syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin,syscoin/syscoin