Use hspec's parallel evaluation (#65)

Author: MaximilianAlgehed

constrained-generators.cabal

@@ -138,6 +138,8 @@ test-suite constrained-tests
     -Wredundant-constraints
     -Wunused-packages
     -rtsopts
+    -threaded
+    -with-rtsopts=-N
 
   build-depends:
     QuickCheck >= 2.15.0.1,

test/Tests.hs

@@ -9,6 +9,6 @@ import Test.Hspec
 main :: IO ()
 main = do
   nightly <- isJust <$> lookupEnv "NIGHTLY"
-  hspec $ do
+  hspec $ parallel $ do
     Tests.tests nightly
     Graph.tests nightly