Update maintenance-table

Author: MarcoFalke

_includes/posts/maintenance-table.md

@@ -1,6 +1,6 @@
-| 0.15 | 2017-09-15 | 2018-10-03  | 2019-08-01 |
 | 0.16 | 2018-02-26 | 2019-05-02  | 2020-02-01 |
 | 0.17 | 2018-10-03 | 2019-11-24  | 2020-08-01 |
-| 0.18 | 2019-05-02 | after v0.20 | TBA        |
+| 0.18 | 2019-05-02 | 2020-06-03  | 2021-02-01 |
 | 0.19 | 2019-11-24 | after v0.21 | TBA        |
-| 0.20 | TBA*       | TBA         | TBA        |
+| 0.20 | 2020-06-03 | after v0.22 | TBA        |
+| 0.21 | TBA*       | TBA         | TBA        |