[parser] fix typing for medline

src/PUBMED/Parser.hs

@@ -2,7 +2,7 @@
 
 module PUBMED.Parser where
 
-import Control.Lens ((^?), (^.), (^..), only, to, ix, prism', Prism')
+import Control.Lens ((^?), (^.), (^..), only, to, ix, prism', Prism', Traversal')
 import Data.Maybe (catMaybes, fromMaybe)
 import Data.Time (UTCTime(..))
 import Data.Time.Segment (jour)
@@ -76,6 +76,7 @@ parsePubMed txt = catMaybes $ txt ^.. pubmedArticle . to pubMed
                        <*> el ^? article . to pubMedArticle
                        <*> el ^? pubDate . to pubMedDate
       where
+        medline :: Traversal' TTL.Element TTL.Element
         medline = namedEl "MedlineCitation"
         article = medline . namedEl "Article"
         articleId = medline . namedEl "PMID"