add warning

Author: joshgoebel

src/highlight.js

@@ -28,6 +28,11 @@ https://highlightjs.org/
   }
 
 }(function(hljs) {
+
+  var warn = console.warn || console.log;
+  warn("Verion 9 of Highlight.js has reached EOL and is no longer supported. Please upgrade to version 10.");
+
+
   // Convenience variables for build-in objects
   var ArrayProto = [],
       objectKeys = Object.keys;