minor mods to poex contract

contracts/examples/ProofOfExistence.sol

-// Proof of Existence contract, version 3
-contract ProofOfExistence3 {
+import "../Rejector.sol";
+
+/*
+ * Proof of Existence example contract
+ * see https://medium.com/zeppelin-blog/the-hitchhikers-guide-to-smart-contracts-in-ethereum-848f08001f05
+ */
+contract ProofOfExistence is Rejector {
 
   mapping (bytes32 => bool) proofs;
 

migrations/2_deploy_contracts.js

 module.exports = function(deployer) {
   deployer.deploy(PullPaymentBid);
   deployer.deploy(BadArrayUse);
+  deployer.deploy(ProofOfExistence);
   deployer.deploy(Bounty);
   deployer.deploy(Ownable);
   deployer.deploy(LimitFunds);