Remove or shorten decimal places from aria-valuenow in meter example

[JAWS-test]

The meter example has about 15 decimal places. The output of the many decimal places is pointless and leads to an excessively detailed output in the screen reader

https://w3c.github.io/aria-practices/examples/meter/meter.html

[JAWS-test]

Just for information: JAWS support of the example is poor, but this is due to JAWS and not the example, see FreedomScientific/standards-support#419