Barometer: update fixed point values to match datasheets for fractional digit accuracy

[rwaldron]

To better understand what needs to be done here, take a look at this example from the Thermometer class:

• https://github.com/rwaldron/johnny-five/blob/master/lib/thermometer.js#L480-L499

And the corresponding tests:

• https://github.com/rwaldron/johnny-five/blob/master/test/thermometer.js#L692

Use the digits.fractional(value) function to get the number of fractional digits in a given value.

[rwaldron]

Sorry for the confusion here, I filed this from a mobile device and I fat fingered a few incorrect labels.