reduced landing page image file sizes

Author: trevorcampbell

docs/404.html

@@ -11,15 +11,15 @@
   <meta property="og:title" content="Page not found |  Data Science" />
   <meta property="og:type" content="book" />
   <meta property="og:url" content="https://datasciencebook.ca" />
-  <meta property="og:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.png" />
+  <meta property="og:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.jpg" />
   <meta property="og:description" content="This is a textbook for teaching a first introduction to data science." />
 
 
   <meta name="twitter:card" content="summary" />
   <meta name="twitter:title" content="Page not found |  Data Science" />
 
   <meta name="twitter:description" content="This is a textbook for teaching a first introduction to data science." />
-  <meta name="twitter:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.png" />
+  <meta name="twitter:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.jpg" />
 
 <meta name="author" content="Tiffany Timbers, Trevor Campbell, and Melissa Lee   Foreword by Roger Peng" />
 
@@ -519,7 +519,7 @@
       <div class="body-inner">
         <div class="book-header" role="navigation">
           <h1>
-            <i class="fa fa-circle-o-notch fa-spin"></i><a href="./"><p><img src="img/ds-a-first-intro-graphic.png" /><br />
+            <i class="fa fa-circle-o-notch fa-spin"></i><a href="./"><p><img src="img/ds-a-first-intro-graphic.jpg" /><br />
 Data Science</p></a>
           </h1>
         </div>

docs/Getting-started-with-version-control.html

@@ -11,15 +11,15 @@
   <meta property="og:title" content="Chapter 12 Collaboration with version control |  Data Science" />
   <meta property="og:type" content="book" />
   <meta property="og:url" content="https://datasciencebook.ca" />
-  <meta property="og:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.png" />
+  <meta property="og:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.jpg" />
   <meta property="og:description" content="This is a textbook for teaching a first introduction to data science." />
 
 
   <meta name="twitter:card" content="summary" />
   <meta name="twitter:title" content="Chapter 12 Collaboration with version control |  Data Science" />
 
   <meta name="twitter:description" content="This is a textbook for teaching a first introduction to data science." />
-  <meta name="twitter:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.png" />
+  <meta name="twitter:image" content="https://datasciencebook.ca/img/ds-a-first-intro-graphic.jpg" />
 
 <meta name="author" content="Tiffany Timbers, Trevor Campbell, and Melissa Lee   Foreword by Roger Peng" />
 
@@ -519,7 +519,7 @@
       <div class="body-inner">
         <div class="book-header" role="navigation">
           <h1>
-            <i class="fa fa-circle-o-notch fa-spin"></i><a href="./"><p><img src="img/ds-a-first-intro-graphic.png" /><br />
+            <i class="fa fa-circle-o-notch fa-spin"></i><a href="./"><p><img src="img/ds-a-first-intro-graphic.jpg" /><br />
 Data Science</p></a>
           </h1>
         </div>