title: npm yarn install failure in ubuntun
body: <p>I try to install yarn in ubuntun but fail:</p>
  <pre><code>$ npm install -g yarn
  npm ERR! code UNABLE_TO_GET_ISSUER_CERT_LOCALLY
  npm ERR! errno UNABLE_TO_GET_ISSUER_CERT_LOCALLY
  npm ERR! request to https://registry.npmjs.org/yarn failed, reason: unable to get local issuer certificate
  </code></pre>
  <p>How can I fix this issue!</p>