Forge Mixin Fix

Alot of mods use Mixin, however other mods like OpenComputers can conflict with it (Unless you're using SpongeForge).

The error is: java.lang.ClassCircularityError: scala/Predef$

Mixin doesn't use Scala however it still has to be excluded by its' changes. This fix has been added to SpongeForge but some people won't want to use it so this is what this mod is for.