repl: fix deprecation code

This slipped through while landing.
Ref: nodejs#15136

Author: BridgeAR

lib/repl.js

@@ -694,7 +694,7 @@ REPLServer.prototype.setPrompt = function setPrompt(prompt) {
 REPLServer.prototype.turnOffEditorMode = util.deprecate(
   function() { _turnOffEditorMode(this); },
   'REPLServer.turnOffEditorMode() is deprecated',
-  'DEP00XX');
+  'DEP0078');
 
 // A stream to push an array into a REPL
 // used in REPLServer.complete