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/Types.hs

@@ -24,7 +24,8 @@ import Network.HTTP.Types.Header (Header, hContentType)
 import Data.Tree
 
 import PostgREST.RangeQuery (NonnegRange)
-import Protolude
+import Protolude            hiding (toS)
+import Protolude.Conv       (toS)
 
 -- | Enumeration of currently supported response content types
 data ContentType = CTApplicationJSON | CTSingularJSON