new rule: mapStateToProps-prefer-hoisted

[DianaSuvorova]

as per discussion in #20

[lencioni]

It might be worth mentioning here that while this is "correct" in the eyes of this rule, it is still problematic for performance.

[DianaSuvorova]

need to make sure this case is flagged correctly as well.

const mapStateToProps = (state) => (
  {
    aProp: state.aProp,
    constProp: []
  }
);

Update error msg to remove comma:

constant arrays, and objects should be initialized outside of mapStateToProps

[DianaSuvorova]

@lencioni I am going to call it a feature and close #20. Thanks a lot for the idea and let me know if you have more on improving this plugin.

Thanks,
Diana

[lencioni]

Thanks for implementing it so quickly! 💖