vm: change ContextifyScript to Script in comment

Reading the comment at the top of the vm.js, I think that
ContextifyScript should perhaps just be Script.

PR-URL: https://github.com/nodejs/node/pull/8415
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Franziska Hinkelmann <franzih@chromium.org>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/vm.js

@@ -4,8 +4,8 @@ const binding = process.binding('contextify');
 const Script = binding.ContextifyScript;
 
 // The binding provides a few useful primitives:
-// - ContextifyScript(code, { filename = "evalmachine.anonymous",
-//                            displayErrors = true } = {})
+// - Script(code, { filename = "evalmachine.anonymous",
+//                  displayErrors = true } = {})
 //   with methods:
 //   - runInThisContext({ displayErrors = true } = {})
 //   - runInContext(sandbox, { displayErrors = true, timeout = undefined } = {})