$ git clone -b 1.8.9 --depth 1 https://github.com/MinecraftForge/MinecraftForge forge2
Cloning into 'forge2'...
remote: Counting objects: 1285, done.
remote: Compressing objects: 100% (1165/1165), done.
remote: Total 1285 (delta 121), reused 504 (delta 55), pack-reused 0
Receiving objects: 100% (1285/1285), 1.46 MiB | 0 bytes/s, done.
Resolving deltas: 100% (121/121), done.
[vincent@vincent-arch mods]$ cd forge2
[vincent@vincent-arch forge2]$ ./gradlew clean setupForge
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true
To honour the JVM settings for this build a new JVM will be forked. Please consider using the daemon: https://docs.gradle.org/2.7/userguide/gradle_daemon.html.
This mapping 'stable_20' was designed for MC 1.8.8! Use at your own peril.
#################################################
         ForgeGradle 2.1-SNAPSHOT-da90449
  https://github.com/MinecraftForge/ForgeGradle
#################################################
               Powered by MCP unknown
             http://modcoderpack.com
         by: Searge, ProfMobius, Fesh0r,
         R4wk, ZeuX, IngisKahn, bspkrs
#################################################
/home/vincent/mods/forge2/jsons/1.8.9-dev.json could not be parsed

FAILURE: Build failed with an exception.

* What went wrong:
A problem occurred configuring root project 'forge'.
> java.io.FileNotFoundException: Inherited json file (null) not found! Maybe you are running in offline mode?

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 6.867 secs