Build failed--Serious Problem PLEASE HELP

Im trying to make a cloud dimension mod and I just made a new block and a new dimension and I want to test it out, but when I go to run a test environment, the console goes crazy. It says:

Executing gradle command: clean build
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         ForgeGradle 2.2-SNAPSHOT-0447b4e        
  https://github.com/MinecraftForge/ForgeGradle  
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               Powered by MCP unknown               
             http://modcoderpack.com             
         by: Searge, ProfMobius, Fesh0r,         
         R4wk, ZeuX, IngisKahn, bspkrs           
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:clean UP-TO-DATE
:deobfCompileDummyTask
:getVersionJson
:extractUserdev UP-TO-DATE
:downloadClient SKIPPED
:downloadServer SKIPPED
:splitServerJar SKIPPED
:mergeJars SKIPPED
:applyBinaryPatches SKIPPED
:deobfProvidedDummyTask
:extractDependencyATs SKIPPED
:extractMcpData SKIPPED
:extractMcpMappings SKIPPED
:genSrgs FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':genSrgs'.
> joptsimple/internal/Strings : Unsupported major.minor version 51.0
* 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: 10.633 secs
Task completed with return code 1 in 11133 milliseconds

So I guess the :gensrgs failed. What is that and how do I fix it?