This code has moved into the ProBuilder repository under "Samples~". See https://github.com/Unity-Technologies/com.unity.probuilder
Example code for the Package Manager version of ProBuilder.
Prior to importing these assets, please make sure ProBuilder is installed. See installing ProBuilder for more information.
Using the command line:
cd ~/MyUnityProject/Assets
git clone https://github.com/Unity-Technologies/ProBuilder-API-Examples.git