Fixes #157: Incorrect Fahrenheit temperature rounding

[ronaldheft]

Siri / HomeKit occasionally displays the incorrect temperature when the Nest's units are set to Fahrenheit.

For example, "Hey Siri set the temperature to 72-degrees" -> "Ok, I set the temperature to 71.6-degrees Fahrenheit."

This issue is a result of the "minStep" property being set to 0.5. Since HomeKit operates exclusively in Celsius, with minStep being set, HomeKit is rounding the Fahrenheit value in to the nearest 0.5 degree Celsius before setting the value, which can results in some weird rounding when converting Celsius back to Fahrenheit.

For the above: 72-degress F = 22.22-degrees C. HomeKit rounds that to 22-degrees C, which is ends up being 71.6-degrees F when converted back.

This minStep restriction is unnecessary for Fahrenheit temperatures since the when setting the temperature, the temperature is already rounded to nearest valid unit the Nest API will accept. Additionally, HomeKit is limited to 1-degree increments for Fahrenheit units.

Fixes #157

[chrisjshull]

Great news! I have taken up maintenance of the homebridge-nest plugin in npm. The source code now lives at https://github.com/chrisjshull/homebridge-nest/. To update to the latest version of homebridge-nest, simply run npm update -g homebridge-nest.

I believe I've merged this patch into that repo. If not, please submit a new PR there.

[ronaldheft]

@chrisjshull Awesome, just updated!