docs: typo fix

Author: thephez

docs/user/masternodes/maintenance.rst

@@ -222,7 +222,7 @@ Where:
 - ``votingKeyAddr``: An updated voting key address, or ``""`` to use the last on-chain voting key
 - ``payoutAddress``: An updated Dash address for owner payments, or ``""`` to use the currently
   active payout address
-- ``feeSourceAddress`` (optional): An address used to fund ProTx fee. ``PayoutAddress`` will be used
+- ``feeSourceAddress`` (optional): An address used to fund ProTx fee. ``payoutAddress`` will be used
   if not specified.
 
 Example to update payout address::