do not overwrite metadata, instead extend the array

Author: ThomasKranitsas

src/services/ChallengeService.js

@@ -1914,6 +1914,16 @@ async function update (currentUser, challengeId, data, isFull) {
 
   delete data.attachments
   delete data.terms
+  const finalMetadata = [...challenge.metadata || []]
+  _.each(data.metadata || [], (rec) => {
+    const existingMeta = _.findIndex(finalMetadata, m => m.name === rec.name)
+    if (existingMeta > -1) {
+      finalMetadata[existingMeta].value = rec.value
+    } else {
+      finalMetadata.push(rec)
+    }
+  })
+  data.metdata = finalMetadata
   _.assign(challenge, data)
   if (!_.isUndefined(newAttachments)) {
     challenge.attachments = newAttachments