fix(transport_helper): fix typo in database mapping of "Segment"

lib/transport_helper.dart

@@ -185,7 +185,7 @@ class Segment {
 
   Map<String, Object?> toMap() {
     return {
-      "startPoint": startPoint.id,
+      "startpoint": startPoint.id,
       "endpoint": endPoint.id,
       "starttime": startTime,
       "endtime": endTime,