I also had the same issue and I found what's wrong.
Two executable files "launcher" and "micronucleus" were built for x86 32bit platforms.
So I had to build them on my ARM board with following steps.
sudo apt install git
git clone https://github.com/micronucleus/micronucleus
cd micronucleus/commandline/
sudo apt install libusb-dev
make
cp micronucleus ~/.arduino15/packages/digistump/tools/micronucleus/2.0a4
sudo cp 49-micronucleus.rules /etc/udev/rules.d/.
git clone https://github.com/digistump/avr-dummy
cd avr-dummy
make
cp avrdude ~/.arduino15/packages/digistump/tools/micronucleus/2.0a4/launcher
Now I can upload my sketch file to Digispark board from my ARM board (ODROID-XU4).
I'm using the latest 1.8.2 Linux ARM Arduino IDE.
Plug in device now... (will timeout in 60 seconds)
> Please plug in the device ...
> Press CTRL+C to terminate the program.
> Device is found!
connecting: 16% complete
connecting: 22% complete
connecting: 28% complete
connecting: 33% complete
> Device has firmware version 1.6
> Available space for user applications: 6012 bytes
> Suggested sleep time between sending pages: 8ms
> Whole page count: 94 page size: 64
> Erase function sleep duration: 752ms
parsing: 50% complete
> Erasing the memory ...
erasing: 55% complete
erasing: 60% complete
erasing: 65% complete
> Starting to upload ...
writing: 70% complete
writing: 75% complete
writing: 80% complete
> Starting the user app ...
running: 100% complete
>> Micronucleus done. Thank you!
I attach two binaries for other ARM users. Just copy two files to ~~~~/2.0a4 directory.
It should work with other 32bit ARM boards.
Happy coding on ARM PC ! 
bin_arm.zip (25.1 KB)