New getcoinsupply RPC is returning a JSON object instead of a numeric

[davecgh]

As the title indicates, the new getcoinsupply RPC command is returning a JSON object instead of a numeric value which is inconsistent with every other command:

$ dcrctl --testnet getcoinsupply
{
  "coinsupply": 41607334358723
}

Compare that to:

$ dcrctl --testnet getnetworkhashps
786150989
 $ dcrctl --testnet getblockcount
13464
$ dcrctl --testnet getconnectioncount
8
$ dcrctl --testnet getcurrentnet
118030347