There's a link to a driver that's supposed to be compatible with Sierra at that mblock.cc link. The wch.cn driver is apparently not compatible with Sierra, though likely WCH, the manufacturer of the CH340, will fix that issue eventually.
It's kind of ironic that Mac is supposed to be "It just works" but there have been so many reports of Arduino issues with El Capitan and Sierra.
UPDATE 2018-03-24:
The manufacturer of the CH340 fixed this incompatibility a long time ago. I don't recommend anyone to use the 3rd party drivers anymore. Use the official drivers downloaded from the manufacturer's website:
http://www.wch.cn/download/CH341SER_MAC_ZIP.html