Make the package strong-mode clean.

test/hex_test.dart

Index: test/hex_test.dart
diff --git a/test/hex_test.dart b/test/hex_test.dart
index f52edaf28d741abf7fd484721dd5816179ff3e1d..837085f6bc4a04f1361656c1eca4801219fd81f6 100644
--- a/test/hex_test.dart
+++ b/test/hex_test.dart
@@ -16,8 +16,8 @@ void main() {
 
     group("with chunked conversion", () {
       test("converts byte arrays to hex", () {
-        var results = [];
-        var controller = new StreamController(sync: true);
+        var results = <String>[];
+        var controller = new StreamController<String>(sync: true);
         controller.stream.listen(results.add);
         var sink = hex.encoder.startChunkedConversion(controller.sink);
 
@@ -29,8 +29,8 @@ void main() {
       });
 
       test("handles empty and single-byte lists", () {
-        var results = [];
-        var controller = new StreamController(sync: true);
+        var results = <String>[];
+        var controller = new StreamController<String>(sync: true);
         controller.stream.listen(results.add);
         var sink = hex.encoder.startChunkedConversion(controller.sink);
 
@@ -67,11 +67,11 @@ void main() {
     });
 
     group("with chunked conversion", () {
-      var results;
+      List<List<int>> results;
       var sink;
       setUp(() {
         results = [];
-        var controller = new StreamController(sync: true);
+        var controller = new StreamController<List<int>>(sync: true);
         controller.stream.listen(results.add);
         sink = hex.decoder.startChunkedConversion(controller.sink);
       });