Update to protolude 0.3.0

The good part is that protolude 0.3.0 builds with GHC 8.10.

The bad part is that this change is a bit painful:
- the default `toS` has changed to no longer convert to and from ByteString
- similarly, `show` no longer outputs ByteString

The changes here are pretty much minimal to keep things compiling; I didn't
see a nice way to work with the new ConvertText class, even though `toUtf8`
seems like it might help if used besides `toS` at just the right spots.

test/Main.hs

@@ -16,7 +16,8 @@ import PostgREST.App         (postgrest)
 import PostgREST.Config      (AppConfig (..))
 import PostgREST.DbStructure (getDbStructure, getPgVersion)
 import PostgREST.Types       (pgVersion95, pgVersion96)
-import Protolude             hiding (toList)
+import Protolude             hiding (toList, toS)
+import Protolude.Conv        (toS)
 import SpecHelper
 
 import qualified Feature.AndOrParamsSpec