made remaining public fallback functions external (#1080)

contracts/examples/SimpleSavingsWallet.sol

@@ -24,7 +24,7 @@ contract SimpleSavingsWallet is Heritable {
   /**
    * @dev wallet can receive funds.
    */
-  function () public payable {
+  function () external payable {
     emit Received(msg.sender, msg.value, address(this).balance);
   }
 

contracts/payment/SplitPayment.sol

@@ -32,7 +32,7 @@ contract SplitPayment {
   /**
    * @dev payable fallback
    */
-  function () public payable {}
+  function () external payable {}
 
   /**
    * @dev Claim your share of the balance.