Add payable to MultisigWalletMock()

contracts/test-helpers/MultisigWalletMock.sol

@@ -5,7 +5,7 @@ contract MultisigWalletMock is MultisigWallet {
   uint public totalSpending;
 
   function MultisigWalletMock(address[] _owners, uint _required, uint _daylimit)
-    MultisigWallet(_owners, _required, _daylimit) { }
+    MultisigWallet(_owners, _required, _daylimit) payable { }
 
   function changeOwner(address _from, address _to) external { }