extrinsics: fix `Vec<AccountId>` args
Created by: ascjones
Where a message or a constructor accepts a Vec<AccountId>
as an argument e.g multisig
, the custom decoder should be used so that SS58 format. e.g.
contract instantiate \
--args 2 [5GrwvaEF5zXb26Fz9rcQpDWS57CtERHpNehXCPcNoHGKutQY,5FHneW46xGXgs5mUiveU4sbTyGBzmstUspZC92UhjJM694ty] \
--suri //Alice \
--dry-run