fix returns

docs/solidity-by-example.rst

@@ -851,7 +851,7 @@ The full contract
         }
 
         /// builds a prefixed hash to mimic the behavior of eth_sign.
-        function prefixed(bytes32 hash) internal pure return (bytes32) {
+        function prefixed(bytes32 hash) internal pure returns (bytes32) {
             return keccak256("\x19Ethereum Signed Message:\n32", hash);
         }
     }