simple array without changes seen as a change

## Version
3.15

## Steps to reproduce

    let test = { '4': ['Bobby','Sam'] };
    let cs = new Changeset(test);

    cs.set('4', ['Bobby','Sam']);

    console.log('cs.isDirty', cs.isDirty);

## Expected Behavior

console log outputs false

## Actual Behavior

console log outputs true
