misc(test): support latest version of pkg:test, fix deprecations

pkgs/markdown/pubspec.yaml

diff --git a/pkgs/markdown/pubspec.yaml b/pkgs/markdown/pubspec.yaml
index 414bc67..b4423a9 100644
--- a/pkgs/markdown/pubspec.yaml
+++ b/pkgs/markdown/pubspec.yaml
@@ -22,5 +22,5 @@
   html: '>=0.12.2 <0.14.0'
   js: '^0.6.1'
   path: '^1.3.1'
-  test: '^0.12.4+1'
+  test: '>=0.12.42 <2.0.0'
   yaml: '^2.1.8'

pkgs/markdown/test/blns_test.dart

diff --git a/pkgs/markdown/test/blns_test.dart b/pkgs/markdown/test/blns_test.dart
index 393fc0a..383e112 100644
--- a/pkgs/markdown/test/blns_test.dart
+++ b/pkgs/markdown/test/blns_test.dart
@@ -23,7 +23,7 @@
   for (var str in blns) {
     test('blns string $index', () {
       var result = markdownToHtml(str);
-      expect(result, new isInstanceOf<String>());
+      expect(result, const TypeMatcher<String>());
     });
     index++;
   }
@@ -32,7 +32,7 @@
   for (var str in blns) {
     test('blns string $index w/ gitHubWeb', () {
       var result = markdownToHtml(str, extensionSet: ExtensionSet.gitHubWeb);
-      expect(result, new isInstanceOf<String>());
+      expect(result, const TypeMatcher<String>());
     });
     index++;
   }

pkgs/markdown/test/document_test.dart

diff --git a/pkgs/markdown/test/document_test.dart b/pkgs/markdown/test/document_test.dart
index 88659d0..78290f7 100644
--- a/pkgs/markdown/test/document_test.dart
+++ b/pkgs/markdown/test/document_test.dart
@@ -11,8 +11,10 @@
       var document = new Document(encodeHtml: false);
       var result = document.parseInline('< &');
       expect(result, hasLength(1));
-      expect(result[0], new isInstanceOf<Text>());
-      expect((result[0] as Text).text, equals('< &'));
+      expect(
+          result[0],
+          const TypeMatcher<Text>()
+              .having((e) => e.text, 'text', equals('< &')));
     });
   });
 }