add og:description

docs/2017/index.html

@@ -13,9 +13,9 @@
 <meta property="og:locale" content="en_US" />
 <meta property="og:site_name" content="Open Source Survey" />
 <meta property="og:image" content="http://opensourcesurvey.org/assets/img/card.png" />
+<meta property="og:description" content="GitHub's 2017 Open Source Survey" />
 <meta name="twitter:card" content="summary_large_image" />
 <meta name="twitter:site" content="@github" />
-<meta name="twitter:image" content="http://opensourcesurvey.org/assets/img/card.png">
 <script type="application/ld+json">
 {"@context":"http://schema.org","@type":"WebPage","headline":"Open Source Survey","image":"/assets/img/card.png","publisher":{"@type":"Organization","logo":{"@type":"ImageObject","url":"https://assets-cdn.github.com/images/modules/open_graph/github-logo.png"}},"url":"/2017/"}</script>
 <!-- End Jekyll SEO tag -->