Update images (#146)

_config.yml

@@ -57,7 +57,7 @@ parse:
       <div id="email-modal" class="modal">
         <iframe name="ghost-result" style="display: none;"></iframe>
         <form class="modal-content" id="email-form" novalidate="">
-          <img src="https://static.premai.io/book/book-cover.png" alt="book cover" />
+          <img src="https://static.premai.io/book/book-cover-2.jpg" alt="book cover" />
           <div class="modal-text">
             <h1>Enter your email to access this book for free</h1>
             <div>

prem_theme/layout.html

@@ -3,7 +3,7 @@
 <meta property="og:site_name" content="The State of Open Source AI" />
 <meta property="og:title" content="{{ title }}" />
 <meta property="og:type" content="book" />
-<meta property="og:image" content="https://static.premai.io/book/marketing/twitter--book.png" />
+<meta property="og:image" content="https://static.premai.io/book/marketing/twitter--book-2.jpg" />
 <meta property="og:url"
     content="https://book.premai.io/state-of-open-source-ai/{{ '' if pagename == 'index' else pagename }}" />
 <meta property="og:description" content="Clarity in the current fast-paced mess of Open Source innovation" />