Security: Move supported horizon to 1.3.1

Author: tdewey-rpi

SECURITY.md

@@ -6,7 +6,8 @@ Only listed versions receive active support, and $HEAD may be changed at any tim
 
 | Version | Supported          |
 | ------- | ------------------ |
-| 1.3.0   | ✅ |
+| 1.3.1   | ✅ |
+| 1.3.0   |  |
 | 1.2.1   |  |
 | 1.2.0   |  |
 | 1.1.1   |  |