Ignore "traverse_" from hlint

In https://travis-ci.org/reflex-frp/reflex/builds/616304027 we notice
that hlint suggests:

   linting file src/Reflex/Spider/Internal.hs...
   reflex-0.6.2.4/src/Reflex/Spider/Internal.hs:497:13: Warning: Use traverse_
   Found:
     WeakBag.traverse (coincidenceSubscribedSubscribers subscribed)
       $ invalidateSubscriberHeight outerHeight
   Perhaps:
     traverse_ (coincidenceSubscribedSubscribers subscribed)
       $ invalidateSubscriberHeight outerHeight

   1 hint

This suggestion isn’t relevant because we don’t have a “traverse_”
equivalent for WeakBag.traverse. Looking at the code in
Hlint (src/Hint/Monad.hs), it becomes clear that it’s a dumb search
for any usage of “traverse”, regardless of being in the Traversable
typeclass.

What’s less clear is why this used to not be a problem before
recently. This error appears to coincide with an update of hlint from
v2.2.2 to v2.2.4.

To fix this, tell Hlint to ignore “Use traverse_” hints in Reflex.
This can be removed once Hlint is taught to distinguise between
traverse from the Traversable typeclass and from somewhere else.

Author: matthewbauer

test/hlint.hs

@@ -23,6 +23,7 @@ main = do
         , "--ignore=Reduce duplication"
         , "--cpp-define=USE_TEMPLATE_HASKELL"
         , "--ignore=Use tuple-section"
+        , "--ignore=Use traverse_"
         ]
       recurseInto = and <$> sequence
         [ fileType ==? Directory