Low - MiniMeToken.sol updateValueAtNow() optimization

[k4ms]

In 'MiniMeToken.sol' the updateValueAtNow() function adds levels of complexity than can be avoided:

• calling push() is cheaper than increasing the checkpoint length and assigning value to the struct
• too many local variables are used

Proposed implementation:

    function updateValueAtNow(Checkpoint[] storage checkpoints, uint _value) internal  {
        if ((checkpoints.length == 0)
        || (checkpoints[checkpoints.length -1].fromBlock < getBlockNumber())) {
             checkpoints.push(Checkpoint({
                 fromBlock: uint128(getBlockNumber()),
                 value: uint128(_value)
             }));
        } else {
            checkpoints[checkpoints.length-1].value = uint128(_value);     
        }
    }