fixes #610, incorrect help output

lib/src/analyzer/context.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.
 
 import 'package:args/args.dart' show ArgParser, ArgResults;
 import 'package:analyzer/file_system/file_system.dart'
     show ResourceProvider, ResourceUriResolver;
 import 'package:analyzer/file_system/physical_file_system.dart'
     show PhysicalResourceProvider;
@@ skipping 56 matching lines @@
       : summaryPaths = args['summary'] as List<String>,
         dartSdkPath = args['dart-sdk'] ?? getSdkDir().path,
         dartSdkSummaryPath = args['dart-sdk-summary'],
         customUrlMappings = _parseUrlMappings(args['url-mapping']),
         packageRoot = args['package-root'],
         packagePaths = (args['package-paths'] as String)?.split(',') ?? [];
 
   /// Whether to resolve 'package:' uris using the multi-package resolver.
   bool get useMultiPackage => packagePaths.isNotEmpty;
 
-  static ArgParser addArguments(ArgParser parser) {
-    return parser
+  static void addArguments(ArgParser parser) {
+    parser
       ..addOption('summary',
           abbr: 's', help: 'summary file(s) to include', allowMultiple: true)
       ..addOption('dart-sdk', help: 'Dart SDK Path', defaultsTo: null)
       ..addOption('dart-sdk-summary',
           help: 'Dart SDK Summary Path', defaultsTo: null)
       ..addOption('package-root',
           abbr: 'p',
           help: 'Package root to resolve "package:" imports',
           defaultsTo: 'packages/')
       ..addOption('url-mapping',
-          help: '--url-mapping=libraryUri,/path/to/library.dart uses \n'
+          help: '--url-mapping=libraryUri,/path/to/library.dart uses\n'
               'library.dart as the source for an import of of "libraryUri".',
           allowMultiple: true,
           splitCommas: false)
       ..addOption('package-paths',
           help: 'use a list of directories to resolve "package:" imports');
   }
 
   static Map<String, String> _parseUrlMappings(Iterable argument) {
     var mappings = <String, String>{};
     for (var mapping in argument) {
@@ skipping 91 matching lines @@
   return sdk;
 }
 
 /// Creates a [DartUriResolver] that uses the SDK at the given [sdkPath].
 DartUriResolver createSdkPathResolver(String sdkSummaryPath, String sdkPath) {
   var sdk = (sdkSummaryPath != null)
       ? new SummaryBasedDartSdk(sdkSummaryPath, true)
       : _createDirectoryBasedDartSdk(sdkPath);
   return new DartUriResolver(sdk);
 }