Update StandardToken.sol
Update StandardToken.sol

Added increaseApproval and decreaseApproval to increase / decrease the approval in 1 transaction.
OpenZeppelin/zeppelin-solidity,OpenZeppelin/openzeppelin-contracts,OpenZeppelin/zeppelin-solidity,OpenZeppelin/openzeppelin-contracts,OpenZeppelin/openzeppelin-contracts,OpenZeppelin/zep-solidity,pash7ka/zeppelin-solidity,dmx374/zeppelin-solidity,dmx374/zeppelin-solidity,pash7ka/zeppelin-solidity,OpenZeppelin/zep-solidity