Fix traverse use in tests on old GHCs.

Author: dolio

tests/Tests/Vector.hs

@@ -3,6 +3,8 @@ module Tests.Vector (tests) where
 import Boilerplater
 import Utilities as Util
 
+import Data.Traversable (traverse)
+
 import qualified Data.Vector.Generic as V
 import qualified Data.Vector
 import qualified Data.Vector.Primitive