title: Rollup Error: 'isValidElementType' is not exported by node_modules/react-is/index.js
body: <p>I'm building a bundle with rollUp using styled-components.</p>
  
  <p>My rollup.config.js looks like:</p>
  
  <pre><code>import resolve from 'rollup-plugin-node-resolve'
  import babel from 'rollup-plugin-babel'
  import commonjs from 'rollup-plugin-commonjs'
  export default {
    input: 'src/index.js',
    output: {
      file: 'dist/bundle.js',
      format: 'cjs'
    },
    external: [
      'react',
      'react-proptypes'
    ],
    plugins: [
      resolve({
        extensions: [ '.js', '.json', '.jsx' ]
      }),
      commonjs({
        include: 'node_modules/**'
      }),
      babel({
        exclude: 'node_modules/**'
      })
    ]
  }
  </code></pre>
  
  <p>And I'm receiving</p>
  
  <pre><code>[!] Error: 'isValidElementType' is not exported by node_modules/react-is/index.js
  https://github.com/rollup/rollup/wiki/Troubleshooting#name-is-not-exported-by-module
  node_modules/styled-components/dist/styled-components.es.js (7:9)
  5: import stream from 'stream';
  6: import PropTypes from 'prop-types';
  7: import { isValidElementType } from 'react-is';
              ^
  8: import hoistStatics from 'hoist-non-react-statics';
  </code></pre>
  
  <p>Checking on the node_modules itself react-is is a commonjs module as it can be checked out <a href="https://github.com/facebook/react/blob/master/packages/react-is/npm/index.js" rel="noreferrer">here</a> as well.</p>
  
  <p>Shouldn't  the commonjs plugin take care of it since it is inside node_modules/** ?</p>
  
  <p>Thanks.</p>