quick wording change

lms/templates/courseware/welcome-back.html

 <h2>${chapter_module.display_name}</h2>
 
-<p>You were last in <a href="${prev_section_url}">${prev_section.display_name}</a>.  If you're done with that, choose another section on the left.</p> 
\ No newline at end of file
+<p>You were most recently in <a href="${prev_section_url}">${prev_section.display_name}</a>.  If you're done with that, choose another section on the left.</p>