docs: Update SECURITY.md (#2533)

Signed-off-by: Ian Lewis <[email protected]>

Author: ianlewis

SECURITY.md

@@ -26,13 +26,12 @@ release, and disclosure processes, as well as general security posture.
 ## Supported Versions
 
 The following versions are currently supported and receive security updates.
+Release candidates will not receive security updates.
 
-| Version | Supported          |
-| ------- | ------------------ |
-| 1.6.x   | :white_check_mark: |
-| 1.5.x   | :white_check_mark: |
-| 1.4.x   | :white_check_mark: |
-| <=1.2.x | :x:                |
+| Version  | Supported          |
+| -------- | ------------------ |
+| >= 1.4.x | :white_check_mark: |
+| <=1.3.x  | :x:                |
 
 ## Reporting a Vulnerability