Update SECURITY.md with new supported versions and reporting method (#30

)

The security document (SECURITY.md) was modified to reflect the new supported versions, now from 3.1.x onwards. The previous versions 1.1 and 1.0 are no longer supported. Furthermore, the method for reporting a vulnerability has been changed to using the GitHub Security Advisories tool.

SECURITY.md

@@ -3,12 +3,11 @@
 ## Supported Versions
 
 | Version | Supported          |
-| ------- | ------------------ |
-| 1.1     | :white_check_mark: |
-| 1.0     | :white_check_mark: |
-| < 1.0   | :x: *unstable releases* |
+|---------| ------------------ |
+| 3.1.x+  | :white_check_mark: |
+| < 3.1.x | :x:                |
 
 ## Reporting a Vulnerability
 
-If you think you have found a security issue, DO NOT open an issue.
-You **MUST** submit your issue at https://gitter.im/Spomky/.
+If you think you have found a security issue, **DO NOT open an issue**.
+You MUST use the GitHub Security Advisories tool at https://github.com/Spomky-Labs/web-push/security/advisories.