Adjust language for new security guidelines (#1904)

Author: AlexJerabek

SECURITY.md

@@ -24,7 +24,7 @@ Please include the requested information listed below (as much as you can provid
   * Any special configuration required to reproduce the issue
   * Step-by-step instructions to reproduce the issue
   * Proof-of-concept or exploit code (if possible)
-  * Impact of the issue, including how an attacker might exploit the issue
+  * Impact of the issue, including how a threat actor might exploit the issue
 
 This information will help us triage your report more quickly.