Add orphan Traversable ((,) a) instance in tests on old GHCs

Author: dolio

tests/Tests/Vector.hs

@@ -68,6 +68,11 @@ import Control.Monad.Trans.Writer
 
 -- TODO: test non-IVector stuff?
 
+#if !MIN_VERSION_base(4,7,0)
+instance Traversable ((,) a) where
+  traverse f (a, b) = fmap ((,) a) $ f b
+#endif
+
 testSanity :: forall a v. (COMMON_CONTEXT(a, v)) => v a -> [Test]
 testSanity _ = [
         testProperty "fromList.toList == id" prop_fromList_toList,