Make the package strong-mode clean.

lib/src/hex/encoder.dart

Index: lib/src/hex/encoder.dart
diff --git a/lib/src/hex/encoder.dart b/lib/src/hex/encoder.dart
index a9c66a5a255cb4401de03655001a0bfb2aea6501..ee53dd70b9aed800d00a5e147e75b1edf9babf45 100644
--- a/lib/src/hex/encoder.dart
+++ b/lib/src/hex/encoder.dart
@@ -16,7 +16,8 @@ const hexEncoder = const HexEncoder._();
 ///
 /// This will throw a [RangeError] if the byte array has any digits that don't
 /// fit in the gamut of a byte.
-class HexEncoder extends Converter<List<int>, String> {
+class HexEncoder
+    extends ChunkedConverter<List<int>, String, List<int>, String> {
   const HexEncoder._();
 
   String convert(List<int> bytes) => _convert(bytes, 0, bytes.length);