pkg/string_scanner: code format, expanded dependency constraint on unittest

test/string_scanner_test.dart

Index: test/string_scanner_test.dart
diff --git a/test/string_scanner_test.dart b/test/string_scanner_test.dart
index fcd904aba17d6f652e4ba9610b26d90102ef9b4d..7b00796ce7931c3c2f672097b4119c2c4454ac20 100644
--- a/test/string_scanner_test.dart
+++ b/test/string_scanner_test.dart
@@ -330,8 +330,8 @@ void main() {
     });
 
     test('throws an ArgumentError if the position is beyond the string', () {
-      expect(() => new StringScanner('foo bar', position: 8),
-          throwsArgumentError);
+      expect(
+          () => new StringScanner('foo bar', position: 8), throwsArgumentError);
     });
   });
 }