Log Message:
www/hs-servant: Update to 0.20.1

0.20.1
* Support aeson-2.2 #1695

0.20
* Headers support in UVerb responses #1570 #1571
* Generalize type of Servant.Types.SourceT.source to any foldable #1593
* Make Mime(Un)Render PlainText String instances encode/decode UTF-8 #1645
* Add HasStatus instance for Headers (that defers StatusOf to underlying
  value) #1649
* Make fromSourceIO run in IO #1661
* Some streaming abstractions, like io-streams, require stateful
  initialization. Since all actual call sites of fromSourceIO are in a
  context where IO actions can be executed, these streaming sources can be
  accomodated by having letting fromSourceIO run in IO.
* To migrate your existing FromSourceIO instance, simply put a pure/return
  in front of it.
* Fix the handling of multiple headers with the same name. #1666