[fix] darker green for result urls

searx/static/themes/oscar/less/logicodev/results.less

 }
 
 .external-link {
-    color: @green;
-    font-size: 11px;
-    font-weight:bold;
+    color: @dark-green;
+    font-size: 12px;
 
     a {
         margin-right: 3px;

searx/static/themes/oscar/less/logicodev/variables.less

 @blue: #0088CC; 
 @red: #F35E77;
 @violet: #684898;
+@dark-green: #26a65b;
 @green: #2ecc71;
 @light-green: #01D7D4; 
 @orange: #FFA92F;