Forge Gradle 3 with adding support to other minecraft versions other than 1.13

[fernthedev]

So I keep running into issues with my project setup, causing gradle to make method not found issues etc. even when I downgrade to the one that used to work before. Magically these errors appeared and so switching to ForgeGradle version 3 fixed them, but I can't seem to add 1.8.9 to my dependencies. How do you add 1.8.9? 

My project can be found at https://github.com/Fernthedev/FernAPI though be noted that the build.gradle file with the actual forge dependency and code is found here https://github.com/Fernthedev/FernAPI/tree/master/fernapi-common

It's a sub project because I used to have 3 different modules for spigot bungee and forge and decided to merge them all together 

[fernthedev]

Messed a bit around and now got this error: 

Zip Missing Entry: config.json File: PROJECTDIR\.gradle\caches\forge_gradle\maven_downloader\net\minecraftforge\forge\1.8.9-11.15.1.2318-1.8.9\forge-1.8.9-11.15.1.2318-1.8.9-userdev.jar