title: "Module parse failed: Unexpected token" when added the class field
body: <p>Below TypeScript code (it means that static class fields and other TypeScript features are available) successfully has been built with Webpack: </p>
  
  <pre><code>export default class ConfigRepresentative {
    constructor() {
      console.log('ok');
    }
  }
  </code></pre>
  
  <p>Fails (same if to remove <code>private</code> and <code>static</code>): </p>
  
  <pre><code>export default class ConfigRepresentative {
  
    private static ownInstanceHasBeenCreated: boolean = false;
  
    constructor() {
      console.log('ok');
    }
  }
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>ERROR in ./TypeScriptSource/index.ts 7:10
  Module parse failed: Unexpected token (7:10)
  You may need an appropriate loader to handle this file type.
  | export default class ConfigRepresentative {
  | 
  &gt;   private static ownInstanceHasBeenCreated: boolean = false;
  | 
  |   constructor() {
  </code></pre>
  
  <h2>webpack.config.js</h2>
  
  <pre><code>module.exports = {
  
    entry: './TypeScriptSource/index.ts',
    output: {
      filename: 'index.js',
      path: __dirname,
      libraryTarget: 'umd'
    },
  
    target: 'node',
    mode: 'production',
    watch: true,
  
    module: {
      rules: [
        {
          test: /\.ts?$/,
          use: 'ts-loader',
          exclude: /node_modules/
        }
      ]
    },
    resolve: {
      extensions: ['.ts', '.js']
    }
  };
  </code></pre>
  
  <p>For saving your time on reproducing this problem, I attached the souse files.
  <a href="https://github.com/TypeStrong/ts-loader/files/2567961/error.zip" rel="nofollow noreferrer">error.zip</a></p>