update balance syntax for solidity 0.4.23 (OpenZeppelin#940)

contracts/ownership/HasNoEther.sol

@@ -36,6 +36,6 @@ contract HasNoEther is Ownable {
    * @dev Transfer all Ether held by the contract to the owner.
    */
   function reclaimEther() external onlyOwner {
-    owner.transfer(this.balance);
+    owner.transfer(address(this).balance);
   }
 }