message: change may 2020 HF variable to use the block height instead of time
diff: @@ -156,8 +156,8 @@ struct Params
  int may2019Height;
  /** Nov 15, 2019 actication height */
  int nov2019Height;
  - /** May 15, 2020 MTP activation time will be 12:00:00 UTC */
  - uint64_t may2020ActivationTime;
  + /** May 15, 2020 actication height */
  + int may2020Height;
  /** Nov 15, 2020 MTP activation time will be 12:00:00 UTC */
  uint64_t nov2020ActivationTime;
  };
  