Update class name to not use bootstrap's text-light class

app/assets/stylesheets/pages/convdev_index.scss

@@ -112,7 +112,7 @@ $space-between-cards: 8px;
     margin: 0 0 2px;
   }
 
-  .text-light {
+  .light-text {
     font-size: 13px;
     line-height: 1.25;
     color: $gl-text-color-secondary;

app/views/admin/conversational_development_index/_card.html.haml

@@ -3,7 +3,7 @@
     .convdev-card-title
       %h3
         = card.title
-      .text-light
+      .light-text
         = card.description
     .board-card-scores
       .board-card-score