Maker: Round scaled sensor values

[islemaster]

Requested by curriculum: sensor.value should always return a round number after calling setScale(0, 1023) (which maps the normal 0-1023 range onto a different range). We're okay with the loss of precision inherent in this decision. (one-line spec)

I wrote tests for this here, but to make the actual fix I had to fork johnny-five, because its Sensor component defines its value property in the constructor as a nonconfigurable getter that I can't modify, replace, or override with a subclass.