thanks for the suggestion however I did try to replace in Arduino's preferences:
https://arduino.esp8266.com/stable/pack ... index.json
https://raw.githubusercontent.com/earle ... plate.json
but now I cannot even install esp board.
I was using a manual edited version that worked, try using this url
https://www118.zippyshare.com/d/bO2w1Ba ... index.json
in settings (or preferences.txt) until 3.0.1 gets published
but to be honest: 3.0.0 breaks so many things that I don't know why someone would voluntarily "upgrade", at least wait for 3.0.1 for worst flaws to be fixed.
if you don't believe me, have a look over at github issues. As not even installation works correct, what else to say ...