title: Error when running 'serializer build' in jaguar_serializer
body: <p>I'm trying to use jaguar_serializer to convert my json string to its corresponding model object. I followed the steps as described in <a href="https://github.com/Jaguar-dart/jaguar_serializer" rel="nofollow noreferrer">https://github.com/Jaguar-dart/jaguar_serializer</a>. However, I keep getting this error when I run 'serializer build':</p>
  
  <p><strong>'package:jaguar_generator_config/src/generator.dart': error: line 17: illegal implicit access to receiver 'this'
    _config = loadYaml(new File(configFileName).readAsStringSync());</strong></p>
  
  <p>Here is my user.dart model:</p>
  
  <pre><code>library models.user;
  
  import 'package:jaguar_serializer/serializer.dart';
  
  part 'user.g.dart';
  
  @GenSerializer()
  class UserJsonSerializer extends Serializer&lt;User&gt; with _$UserJsonSerializer {
    User createModel() =&gt; new User();
  }
  
  /// User model
  class User {
    String name;
    int age;
  }
  </code></pre>
  
  <p>And here is my serializer.yaml file:</p>
  
  <pre><code>serializers:
  # Add files with your serializable class here.
  - lib/models/user.dart
  </code></pre>
  
  <p>The library version of the serializer is </p>
  
  <blockquote>
    <p>jaguar_serializer: ^0.3.0</p>
  </blockquote>