Use correct in_ quoting in haddock code block

Follow-up on prowdsponsor/esqueleto#154

Author: qrilka

src/Database/Esqueleto/Internal/Language.hs

@@ -471,7 +471,7 @@ class (Functor query, Applicative query, Monad query) =>
   -- @
   -- select $
   -- 'from' $ \\person -> do
-  -- 'where_' $ person '^.' PersonId ``in_'` 'valList' personIds
+  -- 'where_' $ person '^.' PersonId `'in_`` 'valList' personIds
   -- return person
   -- @
   --