The `clockmaker` script is missing identifiers for more recent Raspberry Pi models

Created by: grempe

The model revision ID's are missing some recent models, causing the clockmaker script to fail on running clockmaker --config:

https://github.com/ntpsec/stratum-1-microserver-howto/blob/master/clockmaker#L67

The New Style additional revision codes are listed here:

https://www.raspberrypi.org/documentation/hardware/raspberrypi/revision-codes/README.md

Without the addition of the revision code for my Raspberry Pi Model 3B+ this script fails when first used:

pi@raspberrypi:~ $ sudo ./clockmaker --config
SBC type is Raspberry Pi
Can't identify SBC version

Adding the following entry allowed the script to work:

"a020d3" : "Pi 3 Model B+",