little bug fix for 2017-03-03-servant-and-db.markdown

[p-alik]

Thank you for the post. Would you apply the patch, please.

$ git diff posts/2017-03-03-servant-and-db.markdown 
diff --git a/posts/2017-03-03-servant-and-db.markdown b/posts/2017-03-03-servant-and-db.markdown
index 6c62dc2..dc181c7 100644
--- a/posts/2017-03-03-servant-and-db.markdown
+++ b/posts/2017-03-03-servant-and-db.markdown
@@ -134,7 +134,7 @@ app' :: Pool Connection -> Logger -> Application
 app' pool logger = serve api $ hoistServer api nt $ createCat' :<|> readCat'
   where
     nt :: H x -> Handler x
-    nt m -> runLogT "api" logger (runReaderT (runH m) pool)
+    nt m = runLogT "api" logger (runReaderT (runH m) pool)