Merge dashpay#6117: docs: update supported versions in SECURITY.md

878bce0 docs: update SECURITY.md supported versions (Kittywhiskers Van Gogh)

Pull request description:

  ## Additional Information

  Updates the supported versions list in `SECURITY.md`

  ## Checklist:

  - [x] I have performed a self-review of my own code **(note: N/A)**
  - [x] I have commented my code, particularly in hard-to-understand areas **(note: N/A)**
  - [x] I have added or updated relevant unit/integration/functional/e2e tests **(note: N/A)**
  - [x] I have made corresponding changes to the documentation
  - [x] I have assigned this pull request to a milestone _(for repository code-owners and collaborators only)_

ACKs for top commit:
  PastaPastaPasta:
    utACK 878bce0
  UdjinM6:
    utACK 878bce0
  knst:
    utACK 878bce0

Tree-SHA512: d941a3ca0792b2f08f68cab562a35d869d8e93f627918a25a9753955b6103d1515899b0ca50ff936c966b9f9fd603e12d27b03267361c8f1030a31f9fffdf2ae

SECURITY.md

@@ -4,9 +4,9 @@
 
 | Version | Supported          |
 | ------- | ------------------ |
-| 0.17    | :white_check_mark: |
-| 0.16    | :white_check_mark: |
-| < 0.16  | :x:                |
+| 21      | :white_check_mark: |
+| 20.1    | :white_check_mark: |
+| < 20.1  | :x:                |
 
 ## Reporting a Vulnerability