Fix linting errors

client/src/pages/activity.vue

@@ -35,10 +35,19 @@
       <h2>Activities go here</h2>
       <div v-if="selectedCategory === HIGHLIGHTS">
         <h3>HIGHLIGHTS</h3>
-        <div v-for="topic in myActivities.topics">
+        <div
+          v-for="topic in myActivities.topics"
+          :key="topic.id"
+        >
           <h4>{{ topic.title }}</h4>
-          <div v-for="module in topic.modules">
-            <div v-for="highlight in module.allHighlights">
+          <div
+            v-for="module in topic.modules"
+            :key="module.id"
+          >
+            <div
+              v-for="highlight in module.allHighlights"
+              :key="highlight.id"
+            >
               <mark
                 class="highlight"
                 :class="[`highlight--${highlight.color}`]"