misc(test): fix dart2 issues

pkgs/markdown/test/common_mark_test.dart

diff --git a/pkgs/markdown/test/common_mark_test.dart b/pkgs/markdown/test/common_mark_test.dart
index 27fd541..1210cf9 100644
--- a/pkgs/markdown/test/common_mark_test.dart
+++ b/pkgs/markdown/test/common_mark_test.dart
@@ -17,8 +17,8 @@
   var tests = loadCommonMarkSections(config.prefix);
 
   var statsFile = getStatsFile(config.prefix);
-  var statsJson = jsonDecode(statsFile.readAsStringSync())
-      as Map<String, Map<String, String>>;
+  var statsJson =
+      jsonDecode(statsFile.readAsStringSync()) as Map<String, dynamic>;
 
   group(config.prefix, () {
     tests.forEach((section, examples) {

pkgs/markdown/tool/stats_lib.dart

diff --git a/pkgs/markdown/tool/stats_lib.dart b/pkgs/markdown/tool/stats_lib.dart
index 398010f..5375666 100644
--- a/pkgs/markdown/tool/stats_lib.dart
+++ b/pkgs/markdown/tool/stats_lib.dart
@@ -25,12 +25,13 @@
   var testFile = new File(p.join(toolDir, '${testPrefix}_tests.json'));
   var testsJson = testFile.readAsStringSync();
 
-  var testArray = jsonDecode(testsJson) as List<Map<String, dynamic>>;
+  var testArray = jsonDecode(testsJson) as List;
 
   var sections = new Map<String, List<CommonMarkTestCase>>();
 
   for (var exampleMap in testArray) {
-    var exampleTest = new CommonMarkTestCase.fromJson(exampleMap);
+    var exampleTest =
+        new CommonMarkTestCase.fromJson(exampleMap as Map<String, dynamic>);
 
     var sectionList =
         sections.putIfAbsent(exampleTest.section, () => <CommonMarkTestCase>[]);