message: Change README.md date for release
  The master build was finally successful though the date needs to be changed.
diff: @@ -92,7 +92,7 @@ version of TensorFlow I/O according to the table below:
  | TensorFlow I/O Version | TensorFlow Compatibility | Release Date |
  | --- | --- | --- |
  -| 0.13.0 | 2.2.x | May 09, 2020 |
  +| 0.13.0 | 2.2.x | May 10, 2020 |
  | 0.12.0 | 2.1.x | Feb 28, 2020 |
  | 0.11.0 | 2.1.x | Jan 10, 2020 |
  | 0.10.0 | 2.0.x | Dec 05, 2019 |
  