removed unused json dependency

icfp2015.cabal

@@ -60,7 +60,7 @@ executable icfp2015
   other-extensions:    OverloadedStrings, DeriveGeneric, DeriveDataTypeable
  
   -- Other library packages from which modules are imported.
-  build-depends:       base >=4.6 && <4.9, hashable >=1.2 && <1.3, containers >=0.5 && <0.6, QuickCheck >=2.7 && <2.9, bytestring >=0.10 && <0.11, aeson >=0.8 && <0.9, json >=0.9 && <0.10, pqueue >=1.3 && <1.4
+  build-depends:       base >=4.6 && <4.9, hashable >=1.2 && <1.3, containers >=0.5 && <0.6, QuickCheck >=2.7 && <2.9, bytestring >=0.10 && <0.11, aeson >=0.8 && <0.9, pqueue >=1.3 && <1.4
 
   -- Directories containing source files.
   hs-source-dirs:       src