Fix pre-existing HintCode.UNNECESSARY_TYPE_CHECK_TRUE (#209)

This prepares for landing https://dart-review.googlesource.com/c/sdk/+/190360 into the analyzer.
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3c2b591..813dfed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,5 @@
+## 2.3.1-dev
+
 ## 2.3.0
 
 * Add the ability to group commands by category in usage text.
diff --git a/pubspec.yaml b/pubspec.yaml
index c5d81a3..ba596b3 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,5 +1,5 @@
 name: args
-version: 2.3.0
+version: 2.3.1-dev
 homepage: https://github.com/dart-lang/args
 description: >-
  Library for defining parsers for parsing raw command-line arguments into a set
diff --git a/test/command_parse_test.dart b/test/command_parse_test.dart
index fb50a8d..b6437c1 100644
--- a/test/command_parse_test.dart
+++ b/test/command_parse_test.dart
@@ -13,7 +13,7 @@
       var parser = ArgParser();
       var command = parser.addCommand('install');
       expect(parser.commands['install'], equals(command));
-      expect(command is ArgParser, isTrue);
+      expect(command, const TypeMatcher<ArgParser>());
     });
 
     test('uses the command parser if given one', () {