Fix the help doc tests.

test/runner/runner_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 @TestOn("vm")
 
 import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:scheduled_test/descriptor.dart' as d;
@@ skipping 47 matching lines @@
 
     --pub-serve=<port>         The port of a pub serve instance serving "test/".
     --pause-after-load         Pauses for debugging before any tests execute.
                                Implies --concurrency=1.
                                Currently only supported for browser tests.
 
 -r, --reporter                 The runner used to print test results.
 
           [compact]            A single line, updated continuously.
           [expanded]           A separate line for each update.
+          [json]               A machine-readable format (see https://goo.gl/0HRhdZ).
 
     --verbose-trace            Whether to emit stack traces with core library frames.
     --js-trace                 Whether to emit raw JavaScript stack traces for browser tests.
     --[no-]color               Whether to use terminal colors.
                                (auto-detected by default)
 """;
 
 void main() {
   useSandbox();
 
@@ skipping 588 matching lines @@
         d.file("test.dart", _success).create();
 
         var test = runTest(["--plain-name", "no match", "test.dart"]);
         test.stderr.expect(
             consumeThrough(contains('No tests match "no match".')));
         test.shouldExit(exit_codes.data);
       });
     });
   });
 }