models: Fixed wrong database mapping for comment source.

models/comment.go

@@ -13,5 +13,5 @@ type Comment struct {
 	FictionalDate time.Time `bson:"fictionalDate"`
 	CreatedDate   time.Time `bson:"createdDate"`
 	EditedDate    time.Time `bson:"editeddDate"`
-	Source        string    `bson:"sources"`
+	Source        string    `bson:"source"`
 }