Update solidity-by-example.rst

highestBidder is the address.
it's highestBid that should be != 0 to be considered as pending return.

It's that right?

docs/solidity-by-example.rst

@@ -272,7 +272,7 @@ activate themselves.
             // money back.
             require(msg.value > highestBid);
 
-            if (highestBidder != 0) {
+            if (highestBid != 0) {
                 // Sending back the money by simply using
                 // highestBidder.send(highestBid) is a security risk
                 // because it could execute an untrusted contract.