Update social card image

Author: dbader

docs/_static/social-card.jpg

@@ -28,8 +28,8 @@
   <meta name="google-site-verification" content="013PxE2_8KX9jdUSC5gr8QsfdxTXr1mFgmD9zplp5II" />
 
   <meta name="twitter:card" content="summary">
-  <meta property="twitter:image" content="https://docs.python-guide.org/_static/python-guide-logo.png">
-  <meta property="og:image" content="https://docs.python-guide.org/_static/python-guide-logo.png">
+  <meta property="twitter:image" content="https://docs.python-guide.org/_static/social-card.jpg">
+  <meta property="og:image" content="https://docs.python-guide.org/_static/social-card.jpg">
   <meta property="og:title" content="{{ title }}{{ titlesuffix }}">
   <meta property="og:type" content="article">
   {%- if metatags is defined %}