Index update to fix conflict bug

topcoder-archive/topcoder-platform-topcoder-x-ui#79

Author: jmgasper

models/Issue.js

@@ -25,7 +25,7 @@ const schema = new mongoose.Schema({
     default: Date.now
   },
   // From topcoder api
-  challengeId: {type: Number, required: false, unique: true},
+  challengeId: {type: Number, required: false, unique: true, sparse: true},
   projectId: {type: mongoose.Schema.Types.ObjectId, ref: 'Project'},
   status: {type: String},
   assignedAt: {type: Date, required: false}