switch off parallel garbage collector (was slowing down execution on the multi-core system)

see https://github.com/commercialhaskell/stack/issues/680

geval.cabal

@@ -1,5 +1,5 @@
 name:                geval
-version:             1.1.1.0
+version:             1.1.1.1
 synopsis:            Machine learning evaluation tools
 description:         Please see README.md
 homepage:            http://github.com/name/project
@@ -67,7 +67,7 @@ library
 executable geval
   hs-source-dirs:      app
   main-is:             Main.hs
-  ghc-options:         -threaded -rtsopts -with-rtsopts=-N
+  ghc-options:         -threaded -rtsopts "-with-rtsopts=-N -qg"
   build-depends:       base
                      , geval
                      , optparse-applicative