adds 1.4.x versions to SECURITY.md

SECURITY.md

@@ -7,6 +7,7 @@ These borg releases are currently supported with security updates.
 | Version | Supported          |
 |---------|--------------------|
 | 2.0.x   | :x: (not released) |
+| 1.4.x   | :white_check_mark: |
 | 1.2.x   | :white_check_mark: |
 | 1.1.x   | :x:                |
 | < 1.1   | :x:                |