title: RegEx in Webpack loader exclude/include config doesn't work
body: <p>I am trying to apply <code>babel-loader</code> to a specific pattern of modules, say <strong>foo.*</strong>, under <strong>node_modules</strong> in addition to my app. </p>
  
  <p>Other modules under <strong>node_modules</strong> should be skipped as usual. First I tried to use negative look-ahead didn't work:</p>
  
  <pre><code>{
    test: /\.js$/,
    exclude: [
      /node_modules\/(?!foo).*/
    ],
    loader: 'babel-loader',
    query: {
      ...
    }
  }, 
  </code></pre>
  
  <p>Then I splited to two loaders and didn't work either:</p>
  
  <pre><code>{
    test: /\.js$/,
    exclude: [
      path.resolve(_path, "node_modules")
    ],
    loader: 'babel-loader',
    query: {
      ...
    }
  }, 
  {
    test: /\.js$/,
    include: [
      /node_modules\/foo.*/
    ],
    loader: 'babel-loader',
    query: {
      ...
    }
  }
  </code></pre>
  
  <p>However, if I use string instead of RegEx, it works for one folder:</p>
  
  <pre><code>include: [
    path.resolve(_path, "node_modules/foo")
  ],
  </code></pre>
  
  <p>This indicates to me the <strong>Regex</strong> is not working as expected.</p>
  
  <p>Has anyone got <strong>RegEx</strong> working in <code>Include/Exclude</code> field?</p>