Fix return value with latest change in pkg/test (#63)

diff --git a/test/trailing_options_test.dart b/test/trailing_options_test.dart
index cdc4227..ce22ad4 100644
--- a/test/trailing_options_test.dart
+++ b/test/trailing_options_test.dart
@@ -17,9 +17,10 @@
       parser = new ArgParser(allowTrailingOptions: true);
     });
 
-    void expectThrows(List<String> args) => expect(
-        () => parser.parse(args), throwsFormatException,
-        reason: "with allowTrailingOptions: true");
+    void expectThrows(List<String> args) {
+      expect(() => parser.parse(args), throwsFormatException,
+          reason: "with allowTrailingOptions: true");
+    }
 
     test('collects non-options in rest', () {
       parser.addFlag('flag');