fixed twitter link for course about pages

lms/templates/portal/course_about.html

@@ -107,7 +107,7 @@
         <header>
           <div class="social-sharing">
             <div class="sharing-message">Share with friends and family!</div>
-            <a href="http://twitter.com/intent/tweet?text=I+just+registered+for+${course.number}+${get_course_about_section(course, 'title')}+through+@edxonline:+http://edx.org/${reverse('about_course', args=[course.id])}" class="share">
+            <a href="http://twitter.com/intent/tweet?text=I+just+registered+for+${course.number}+${get_course_about_section(course, 'title')}+through+@edxonline:+http://www.edx.org${reverse('about_course', args=[course.id])}" class="share">
               <img src="${static.url('images/social/twitter-sharing.png')}">
             </a>
             <a href="http://www.facebook.com/EdxOnline" class="share"> <img src="${static.url('images/social/facebook-sharing.png')}">