anchor.diff:  
     args.add(pkgName);
   
  -  Map<String, String> pubEnv;
  +  var pubEnv = new Map<String, String>.from(_pubEnv);
     if (pubCachePath != null) {
  -    pubEnv = {'PUB_CACHE': pubCachePath};
  +    pubEnv['PUB_CACHE'] = pubCachePath;
     }
   
     var result = await Process.run('pub', args, environment: pubEnv);
  
positive.code: 
  final _versionDownloadRexexp =
      new RegExp(r"^MSG : (?:Downloading |Already cached )([\w-]+) (.+)$");
  
negative.code: }
  
  Future<PubSummary> pkgSummary(String pkgPath, {String pubCachePath}) async {
    var pubEnv = new Map<String, String>.from(_pubEnv);
    if (pubCachePath != null) {
      pubEnv['PUB_CACHE'] = pubCachePath;
    }
  
    log.info('Running `pub upgrade`...');
  