Also, for anyone else trying out this tutorial but are using the latest version of zeppelin-solidity, I have found the following changes helpful.
(1) In HashnodeToken.sol change the filepath to include the ERC20 folder
import 'zeppelin-solidity/contracts/token/ERC20/MintableToken.sol';
(2) If you are unable to deploy the contract because of a gas issue, try updating the gas amount in truffle.js to reflect the limit in ganache. "gas: 6721974"
Hope this helps someone!