1. install digistump support in arduino:
add http://digistump.com/package_digistump_index.json to board manager urls (file -> preferencies ... )
then install digistamp avr boards support in board manager (Tools->Board->Board manager)
then, download latest bootloader for attiny85: https://raw.githubusercontent.com/micronucleus/micronucleus/master/upgrade/releases/upgrade-t85_default.hex
~/.arduino15/packages/digistump/tools/micronucleus/2.0a4/launcher -cdigispark --timeout 60 -Uflash:w:~/tmp/upgrade-t85_default.hex:i
then new micronucleus binary need to be compiled, cose one installed (2.0a4) did not support bootloader version 2.3 and this error happens when you try to upload hex:
Warning: device with unknown new version of Micronucleus detected.
This tool doesn't know how to upload to this new device. Updates may be available.
Device reports version as: 2.3
so lets upgrade micronucleus binary:
mkdir ~/tmp;cd ~/tmp
git clone firstname.lastname@example.org:micronucleus/micronucleus.git
cd micronucleus/commandline/ ; make
mv micronucleus micronucleus.old
cp ~/tmp/micronucleus/commandline/micronucleus .