pietteTech_DHT library does not work with latest Particle OS (redux)

@ScruffeR: Thank you -- all is now well! This method call was not in our original 2017 code (which worked fine), so I guess that DHT>begin() was either added later or at least was not needed way back when.

This may have been the problem with this posting as well:

Anyway - thank you! The problem is solved.