message: docs: Yuchen Dai to manage stable releases in 2020 Q3.
  While there, update details for v1.15.x releases.
diff: @@ -49,6 +49,8 @@ stable releases and sending announcements about them. This role is rotating on a
  | Quarter | Release manager |
  |:-------:|:----------------------------:|
  | 2020 Q1 | Piotr Sikora ([PiotrSikora]) |
  +| 2020 Q2 | Piotr Sikora ([PiotrSikora]) |
  +| 2020 Q3 | Yuchen Dai ([lambdai]) |
  ## Release schedule
  @@ -61,7 +63,7 @@ deadline of 3 weeks.
  | 1.12.0 | 2019/09/30 | 2019/10/31 | +31 days | 2020/10/31 |
  | 1.13.0 | 2019/12/31 | 2020/01/20 | +20 days | 2021/01/20 |
  | 1.14.0 | 2020/03/31 | 2020/04/08 | +8 days | 2021/04/08 |
  -| 1.15.0 | 2020/06/30 | | | |
  +| 1.15.0 | 2020/06/30 | 2020/07/07 | +7 days | 2021/07/07 |
  | 1.16.0 | 2020/09/30 | | | |
  | 1.17.0 | 2020/12/31 | | | |
  