Update docs for system.account (#1944)

docs/start/api.query.subs.md

@@ -25,7 +25,7 @@ If we had a query with parameters, i.e. where we wish to perform a query for a s
 ...
 
 // Subscribe to balance changes for our account
-const unsub = await api.query.system.account(ADDR, ([nonce, balance]) => {
+const unsub = await api.query.system.account(ADDR, ({ nonce, data: balance }) => {
   console.log(`free balance is ${balance.freee} with ${balance.reserved} reserved and a nonce of ${nonce}`);
 });
 ```