[1.8.9] Forge Dev Environment Setup

Hello,

I am trying to setup a Forge dev environment for 1.8.9 but I am running into some problems.  The old process was to use "gradlew setupDecompWorkspace" but apparently that has been deprecated. I tried just skipping that step and having IntelliJ run the gradlew.build file but that doesn't grab the required Minecraft source jar. So I tried using the newest version of gradlew.build from Forge 1.14 (replacing the proper 1.8.9 Forge version in the dependency) and now I'm getting this error: https://gist.github.com/hjongh/e8446387ae71e3e43030b1831f717874 . Not sure whether I screwed things up when I was messing with Gradle beforehand, or the gradle version is too old (2.7).

So my question is, how can I do the setup for 1.8.9 now? Could I just copy a 1.8.9 Minecraft source jar I have from my old mods and use that?