Drop support for old SDK and shelf versions.

lib/src/runner/configuration.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.
 
 library test.runner.configuration;
 
 import 'dart:io';
 import 'dart:math' as math;
 
 import 'package:args/args.dart';
@@ skipping 38 matching lines @@
         allowed: allPlatforms.map((platform) => platform.identifier).toList(),
         defaultsTo: 'vm',
         allowMultiple: true);
     parser.addOption("concurrency",
         abbr: 'j',
         help: 'The number of concurrent test suites run.\n'
             '(defaults to $_defaultConcurrency)',
         valueHelp: 'threads');
     parser.addOption("pub-serve",
         help: 'The port of a pub serve instance serving "test/".',
-        hide: !supportsPubServe,
         valueHelp: 'port');
     parser.addFlag("pause-after-load",
         help: 'Pauses for debugging before any tests execute.\n'
             'Implies --concurrency=1.\n'
             'Currently only supported for browser tests.',
         negatable: false);
     parser.addOption("reporter",
         abbr: 'r',
         help: 'The runner used to print test results.',
         allowed: ['compact', 'expanded'],
@@ skipping 132 matching lines @@
         pubServeUrl = pubServePort == null
             ? null
             : Uri.parse("http://localhost:$pubServePort"),
         concurrency = pauseAfterLoad
             ? 1
             : (concurrency == null ? _defaultConcurrency : concurrency),
         platforms = platforms == null ? [TestPlatform.vm] : platforms.toList(),
         paths = paths == null ? ["test"] : paths.toList(),
         explicitPaths = paths != null;
 }