fixed #175, following vero suggestions (#178)

themes/grass/layouts/contribute/devel.html

@@ -41,13 +41,13 @@ <h3>Quick links</h3>
             </nav>
             <ul class="list-unstyled">
 	            <li><i class="ms ms-grass-gis"></i> &#160;<a href="https://trac.osgeo.org/grass/wiki/HowToContribute" target="_blank">How to contribute</a></li>
-              <li><i class="fas fa-passport"></i> &#160;<a href="https://grasswiki.osgeo.org/wiki/GRASS_GIS_APIs" target="_blank"> API's wiki page</a></li>
+              <li><i class="fa fa-gears"></i> &#160;<a href="https://grasswiki.osgeo.org/wiki/GRASS_GIS_APIs" target="_blank"> API's wiki page</a></li>
               <li><i class="fa fa-file-text"></i> &#160;<a href="https://grass.osgeo.org/programming7/" target="_blank">Developer manual</a></li>              
               <li><i class="fa fa-code"></i> &#160;<a href="https://github.com/OSGeo/grass/blob/master/CONTRIBUTING.md" target="_blank">How to use git to contribute</a></li>
-              <li><i class="fab fa-git-alt"></i> &#160;<a href="https://trac.osgeo.org/grass/wiki/HowToGit" target="_blank">How to use git</a></li>
+              <li><i class="fa fa-code-fork"></i> &#160;<a href="https://trac.osgeo.org/grass/wiki/HowToGit" target="_blank">How to use git</a></li>
 	            <li><i class="fa fa-github"></i> &#160;<a href="https://github.com/OSGeo/grass/" target="_blank"> Source code</a></li>
 	            <li><i class="fa fa-bug"></i> &#160;<a href="https://github.com/OSGeo/grass/issues" target="_blank"> Bug Tracker</a></li>
-	            <li><i class="fas fa-mail-bulk"></i> &#160;<a href="https://lists.osgeo.org/listinfo/grass-dev" target="_blank">GRASS Developers Mailing list</a></li>
+	            <li><i class="fa fa-envelope"></i> &#160;<a href="https://lists.osgeo.org/listinfo/grass-dev" target="_blank">GRASS Developers Mailing list</a></li>
                 </ul>
           </div>
 	 </div>