travis: Update travis to specify which unix variant to build.
travis: Update travis to specify which unix variant to build.

pozetroninc/micropython,tobbad/micropython,MrSurly/micropython,tobbad/micropython,selste/micropython,kerneltask/micropython,bvernoux/micropython,pozetroninc/micropython,adafruit/circuitpython,pozetroninc/micropython,tobbad/micropython,henriknelson/micropython,henriknelson/micropython,bvernoux/micropython,pramasoul/micropython,pramasoul/micropython,pramasoul/micropython,MrSurly/micropython,pramasoul/micropython,MrSurly/micropython,adafruit/circuitpython,tobbad/micropython,selste/micropython,kerneltask/micropython,adafruit/circuitpython,henriknelson/micropython,henriknelson/micropython,kerneltask/micropython,pozetroninc/micropython,MrSurly/micropython,kerneltask/micropython,bvernoux/micropython,selste/micropython,henriknelson/micropython,adafruit/circuitpython,pramasoul/micropython,tobbad/micropython,bvernoux/micropython,MrSurly/micropython,selste/micropython,adafruit/circuitpython,kerneltask/micropython,pozetroninc/micropython,selste/micropython,bvernoux/micropython,adafruit/circuitpython