message: Add WasmMsg::Migrate variant
diff: @@ -109,6 +109,20 @@ pub enum WasmMsg {
  /// optional human-readbale label for the contract
  label: Option<String>,
  },
  + /// Migrates a given contracts to use new wasm code. Passes a MigrateMsg to allow us to
  + /// customize behavior.
  + ///
  + /// Only the contract admin (as defined in wasmd), if any, is able to make this call.
  + ///
  + /// This is translated to a [MsgMigrateContract](https://github.com/CosmWasm/wasmd/blob/v0.14.0/x/wasm/internal/types/tx.proto#L86-L96).
  + /// `sender` is automatically filled with the current contract's address.
  + Migrate {
  + contract_addr: HumanAddr,
  + /// the code_id of the new logic to place in the given contract
  + new_code_id: u64,
  + /// msg is the json-encoded MigrateMsg struct that will be passed to the new code
  + msg: Binary,
  + },
  }
  /// Shortcut helper as the construction of WasmMsg::Instantiate can be quite verbose in contract code
  