title: Wget fails with certificate error
body: <p>As part of an automated build, we run download some code from github. Minimal example:</p>
  
  <pre><code>wget github.com
  </code></pre>
  
  <p>Recently, the command started failing with a certificate error:</p>
  
  <pre><code>URL transformed to HTTPS due to an HSTS policy
  --2017-10-05 11:43:45--  https://github.com/
  Resolving github.com (github.com)... 192.30.253.112, 192.30.253.113
  Connecting to github.com (github.com)|192.30.253.112|:443... connected.
  
  ERROR: cannot verify github.com's certificate, issued by 'CN=DigiCert SHA2 Extended Validation Server CA,OU=www.digicert.com,O=DigiCert Inc,C=US':
    Unable to locally verify the issuer's authority.
  </code></pre>
  
  <p>I tried updating the certificate store, and wget itself:</p>
  
  <pre><code>update-ca-certificates
  apt-get install wget
  </code></pre>
  
  <p>The error is still the same.
  My wget version is GNU Wget 1.17.1, and the OS is Ubuntu 16.04.3.</p>