Unify Library Carpentry logo

Close #155

Author: rgaiacs

_includes/carpentries.html

@@ -29,7 +29,7 @@
 <br/>
 <div class="row">
   <div class="col-md-2" align="center">
-    <a href="{{ site.lc_site }}"><img src="{{ page.root }}/assets/img/lc-icon-black.svg" alt="Library Carpentry logo" /></a>
+    <a href="{{ site.lc_site }}"><img src="{{ page.root }}/assets/img/lc-icon-black.png" alt="Library Carpentry logo" /></a>
   </div>
   <div class="col-md-8">
     <a href="{{ site.lc_site }}">Library Carpentry</a> is made by librarians to help librarians