title: Cannot read property 'fromWIF' of undefined error
body: <p>Im trying create and sign a raw transaction with bitcoinjs-lib.</p>
  <pre><code>const assert = require('assert');
  const ecpair = require('ecpair');
  const bitcoin = require('bitcoinjs-lib');
  var keys    =new bitcoin.ecpair.fromWIF('cMvPQZiG5mLARSjxbBwMxKwzhTHaxgpTsXB6ymx7SGAeYUqF8HAT', bitcoin.networks.testnet);
  </code></pre>
  <p>this is my code and i get error &quot;Cannot read property 'fromWIF' of undefined error&quot; message.
  i think i am making a mistake while adding the libraries.
  bitcoinjs-lib version is 6 and using nodejs.
  thank you.</p>