backport: (parser) use null prototype objects for languages/aliases (#2636)

Author: joshgoebel

src/highlight.js

@@ -33,8 +33,8 @@ https://highlightjs.org/
       objectKeys = Object.keys;
 
   // Global internal variables used within the highlight.js library.
-  var languages = {},
-      aliases   = {};
+  var languages = Object.create(null),
+      aliases   = Object.create(null);
 
   // safe/production mode - swallows more errors, tries to keep running
   // even if a single syntax or parse hits a fatal error