fix(design): update small design issues

src/components/Terms/termsView.scss

@@ -85,7 +85,7 @@
     margin: 0;
     max-width: 150px;
     &:disabled {
-      opacity: 0.7;
+      opacity: 0.3;
     }
   }
 }

src/locales/fr.json

 {
   "common": {
     "title_app": "Ecolyo",
-    "title_challenge": "Défi",
+    "title_challenge": "Défis",
     "title_quiz": "Quiz",
     "title_exploration": "Exploration",
     "title_action": "Action",