It looks like this is becoming a common question. As explained in Dash wont show up as serial port, unless there is a Serial.begin() in the setup of your sketch, the usb serial connection is never told to initialize.
I know this was done to save power for the example sketches, however since most developers try out the sketches before writing their own sketch. I would recommend keeping the Serial.begin() in the setup of all example sketches, with a comment of how/why to remove it, and what the side effect is.