If you get the following error :

micronucleus: library/micronucleus_lib.c:66: micronucleus_connect: Assertion `res >= 4' failed.

Create a file named /etc/udev/rules.d/digispark.rules with the following line in it:

SUBSYSTEM=="usb", ATTR{idVendor}=="16d0", ATTR{idProduct}=="0753", MODE="0660", GROUP="dialout"