Update docs for pressure reading in hectopascals

[caternuson]

This library returns the pressure reading in hectopascals per the CP Design Guide:
https://docs.circuitpython.org/en/latest/docs/design_guide.html#sensor-properties-and-units

Code is here for ref:

Adafruit_CircuitPython_MPL3115A2/adafruit_mpl3115a2.py

Lines 218 to 219 in b32af7d

	# Scale down to hectopascals.
	return pressure / 400.0

Some of the docs are still saying Pascals.

[caternuson]

Example text as well:

Adafruit_CircuitPython_MPL3115A2/examples/mpl3115a2_simpletest.py

Line 30 in df0c9fc

print("Pressure: {0:0.3f} pascals".format(pressure))