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.

src/PostgREST/Parsers.hs

@@ -22,7 +22,9 @@ import Text.ParserCombinators.Parsec hiding (many, (<|>))
 import PostgREST.Error      (ApiRequestError (ParseRequestError))
 import PostgREST.RangeQuery (NonnegRange)
 import PostgREST.Types
-import Protolude            hiding (intercalate, option, replace, try)
+import Protolude            hiding (intercalate, option, replace, toS,
+                             try)
+import Protolude.Conv       (toS)
 
 pRequestSelect :: Text -> Either ApiRequestError [Tree SelectItem]
 pRequestSelect selStr =